Electrode structures

ABSTRACT

A structure for use in an energy storage device, the structure comprising a backbone system extending generally perpendicularly from a reference plane, and a population of microstructured anodically active material layers supported by the lateral surfaces of the backbones, each of the microstructured anodically active material layers having a void volume fraction of at least 0.1 and a thickness of at least 1 micrometer.

FIELD OF THE INVENTION

The present invention generally relates to structures for use in energystorage devices, to energy storage devices incorporating suchstructures, and to methods for producing such structures and energydevices.

BACKGROUND OF THE INVENTION

Rocking chair or insertion secondary batteries are a type of energystorage device in which carrier ions, such as lithium, sodium orpotassium ions, move between an anode electrode and a cathode electrodethrough an electrolyte. The secondary battery may comprise a singlebattery cell, or two more battery cells that have been electricallycoupled to form the battery, with each battery cell comprising an anodeelectrode, a cathode electrode, and an electrolyte.

In rocking chair battery cells, both the anode and cathode comprisematerials into which a carrier ion inserts and extracts. As a cell isdischarged, carrier ions are extracted from the anode and inserted intothe cathode. As a cell is charged, the reverse process occurs: thecarrier ion is extracted from the cathode and inserted into the anode.

FIG. 1 shows a cross sectional view of an electrochemical stack of anexisting energy storage device, such as a non-aqueous, lithium-ionbattery. The electrochemical stack 1 includes a cathode currentcollector 2, on top of which a cathode layer 3 is assembled. This layeris covered by a microporous separator 4, over which an assembly of ananode current collector 5 and an anode layer 6 are placed. This stack issometimes covered with another separator layer (not shown) above theanode current collector 5, rolled and stuffed into a can, and filledwith a non-aqueous electrolyte to assemble a secondary battery.

The anode and cathode current collectors pool electric current from therespective active electrochemical electrodes and enables transfer of thecurrent to the environment outside the battery. A portion of an anodecurrent collector is in physical contact with the anode active materialwhile a portion of a cathode current collector is in contact with thecathode active material. The current collectors do not participate inthe electrochemical reaction and are therefore restricted to materialsthat are electrochemically stable in the respective electrochemicalpotential ranges for the anode and cathode.

In order for a current collector to bring current to the environmentoutside the battery, it is typically connected to a tab, a tag, apackage feed-through or a housing feed-through, typically collectivelyreferred to as contacts. One end of a contact is connected to one ormore current collectors while the other end passes through the batterypackaging for electrical connection to the environment outside thebattery. The anode contact is connected to the anode current collectorsand the cathode contact is connected to the cathode current collectorsby welding, crimping, or ultrasonic bonding or is glued in place with anelectrically conductive glue.

During a charging process, lithium leaves the cathode layer 3 andtravels through the separator 4 as a lithium ion into the anode layer 6.Depending upon the anode material used, the lithium ion eitherintercalates (e.g., sits in a matrix of an anode material withoutforming an alloy) or forms an alloy. During a discharge process, thelithium leaves the anode layer 6, travels through the separator 4 andpasses through to the cathode layer 3. The current conductors conductelectrons from the battery contacts (not shown) to the electrodes orvice versa.

Existing energy storage devices, such as batteries, fuel cells, andelectrochemical capacitors, typically have two-dimensional laminararchitectures (e.g., planar or spiral-wound laminates) as illustrated inFIG. 1 with a surface area of each laminate being roughly equal to itsgeometrical footprint (ignoring porosity and surface roughness).

Three-dimensional batteries have been proposed in the literature as waysto improve battery capacity and active material utilization. It has beenproposed that a three-dimensional architecture may be used to providehigher surface area and higher energy as compared to a two dimensional,laminar battery architecture. There is a benefit to making athree-dimensional energy storage device due to the increased amount ofenergy that may be obtained out of a small geometric area. See, e.g.,Rust et al., WO2008/089110 and Long et. al, “Three-Dimensional BatteryArchitectures,” Chemical Reviews, (2004), 104, 4463-4492.

New anode and cathode materials have also been proposed as ways toimprove the energy density, safety, charge/discharge rate, and cyclelife of secondary batteries. Some of these new high capacity materials,such as silicon, aluminum, or tin anodes in lithium batteries havesignificant volume expansion that causes disintegration and exfoliationfrom its existing electronic current collector during lithium insertionand extraction. Silicon anodes, for example, have been proposed for useas a replacement for carbonaceous electrodes since silicon anodes havethe capacity to provide significantly greater energy per unit volume ofhost material for lithium in lithium battery applications. See, e.g.,Konishiike et al., U.S. Patent Publication No. 2009/0068567; Kasavajjulaet al., “Nano- and Bulk-Silicon-Based Insertion Anodes for Lithium-IonSecondary Cells,” Journal of Power Sources 163 (2007) 1003-1039. Theformation of lithium silicides when lithium is inserted into the anoderesults in a significant volume change which can lead to crack formationand pulverisation of the anode. As a result, capacity of the battery canbe decreased as the battery is repeatedly discharged and charged.

Various strategies have been proposed to overcome the challengespresented by the significant volume changes experienced by siliconanodes as a result of repeated charge and discharge cycles. For example,Bourderau et al. discloses amorphous silicon (Bourderau et al.,“Amorphous Silicon As A Possible Anode Material For Li-Ion Batteries,”Journal of Power Sources 81-82 (1999) 233-236)). Li et al. disclosessilicon nanowires (Li et al., “The Crystal Structural Evolution OfNano-Si Anode Caused By Lithium Insertion And Extraction At RoomTemperature,” Solid State Ionics 135 (2000) 181-191. In NL1015956, SloeYao Kan discloses a porous silicon electrode for a battery. Shin et al.also disclose porous silicon electrodes for batteries (Shin et al.,“Porous Silicon Negative Electrodes For Rechargeable Lithium Batteries,”Journal of Power Sources 139 (2005) 314-320.

Monolithic electrodes, i.e., electrodes comprising a mass of electrodematerial that retains its a shape without the use of a binder, have alsobeen proposed as an alternative to improve performance (gravimetric andvolumetric energy density, rates, etc) over particulate electrodes thathave been molded or otherwise formed into a shape and depend upon aconductive agent or binder to retain the shape of an agglomerate of theparticulate material. A monolithic anode, for example, may comprise aunitary mass of silicon (e.g., single crystal silicon, polycrystallinesilicon, or amorphous silicon) or it may comprise an agglomeratedparticulate mass that has been sintered or otherwise treated to fuse theanodic material together and remove any binder. In one such exemplaryembodiment, a silicon wafer may be employed as a monolithic anodematerial for a lithium-ion battery with one side of the wafer coupled toa first cathode element through a separator, while the other side iscoupled to a second cathode element opposing it. In such arrangements,one of the significant technical challenges is the ability to collectand carry current from the monolithic electrode to the outside of thebattery while efficiently utilizing the space available inside thebattery.

The energy density of conventional batteries may also be increased byreducing inactive component weights and volumes to pack the battery moreefficiently. Current batteries use relatively thick current collectorssince the foils that make up the current collectors are used with aminimum thickness requirement in order to be strong enough to survivethe active material application process. Advantages in performance canbe anticipated if an invention was made in order to separate the currentcollection from processing constraints.

Despite the varied approaches, a need remains for improved batterycapacity and active material utilization.

SUMMARY OF THE INVENTION

Among the various aspects of the present invention is the provision ofthree-dimensional structures for use in energy storage devices such asbatteries, fuel cells, and electrochemical capacitors. Such threedimensional structures comprise a layer of microstructured anodicallyactive material on a lateral surface of a backbone structure, the layercontaining a void fraction that accommodates significant volume changesin the anodically active material as it cycles between a charged and adischarged state. Advantageously, such three-dimensional structures maybe incorporated into two or more battery cells that have been stackedvertically whereby, the shortest distance between the anodically activematerial and the cathode material in a battery cell is measured in adirection that is orthogonal to the direction of stacking of the batterycells (e.g., in X-Y-Z coordinates, if the direction of stacking is inthe Z-direction, the shortest distance between the anodically activematerial and the cathode material is measured in the X- or Y-direction).Such three-dimensional energy storage devices may produce higher energystorage and retrieval per unit geometrical area than conventionaldevices. They may also provide a higher rate of energy retrieval thantwo-dimensional energy storage devices for a specific amount of energystored, such as by minimizing or reducing transport distances forelectron and ion transfer between an anode and a cathode. These devicesmay be more suitable for miniaturization and for applications where ageometrical area available for a device is limited and/or where energydensity requirement is higher than what may be achieved with a laminardevice.

Briefly, therefore, one aspect of the present invention is a structurefor use in an energy storage device. The structure comprises apopulation of microstructured anodically active material layers, wherein(a) members of the population comprise a fibrous or porous anodicallyactive material and have a surface that is substantially perpendicularto a reference plane, (ii) a thickness of at least 1 micrometer measuredin a direction parallel to the reference plane, a height of at least 50micrometers measured in a direction orthogonal to the reference plane,and a void volume fraction of at least 0.1. In addition, the linealdistance between at least two members of the population, measured in adirection parallel to the reference plane, is greater than the maximumheight of any of the layers in the population.

Another aspect of the present invention is a structure for use in anenergy storage device comprising a backbone network comprising a seriesof lateral surfaces. The lateral surfaces are substantiallyperpendicular to a reference plane and have a height of at least 50micrometers measured in a direction that is substantially perpendicularto the reference plane. The structure further comprises a population ofmicrostructured anodically active material layers supported by thelateral surfaces, the greatest lineal distance between at least two ofthe lateral surfaces in the population measured in a direction parallelto the reference plane being greater than the maximum height of any ofthe lateral surfaces in the series. The microstructured anodicallyactive material layers comprise a front surface, a back surface, and afibrous or porous anodically active material, the microstructuredanodically active material layers having a void volume fraction of atleast 0.1 and a thickness between the front and back surfaces of atleast 1 micrometer. The back surface of each such microstructuredanodically active material layer is proximate the lateral surface of thebackbone supporting such microstructured anodically active materiallayer. The front surface of each such microstructured anodically activematerial layer is distal to the lateral surface of the backbonesupporting such microstructured anodically active material layer. Fiberscomprised by a member of the population of microstructured anodicallyactive material layers are attached to and have central axes that aresubstantially parallel to the reference plane at the point of attachmentof the fibers to the back surface of the population member comprisingsuch fibers. Pores comprised by a member of the population ofmicrostructured anodically active material layers have pore openingshaving major axes that are substantially parallel to the referenceplane.

Another aspect of the present invention is an electrochemical stack foruse in an energy storage device. The electrochemical stack comprises, ina stacked arrangement, cathode structures, separator layers and anodestructures, the separator layers being disposed between the anodestructures and the cathode structures, with the direction of stacking ofthe cathode structures, the separator layers, and the anode structuresin the electrochemical stack being parallel to a reference plane. Theanode structures comprise a population of microstructured anodicallyactive material layers wherein (a) members of the population comprise afibrous or porous anodically active material and have (i) a surface thatis substantially perpendicular to the reference plane, (ii) a thicknessof at least 1 micrometer measured in a direction parallel to thereference plane, (iii) a height of at least 50 micrometers measured in adirection orthogonal to the reference plane, and (iv) a void volumefraction of at least 0.1. Additionally, the lineal distance between atleast two members of the population, measured in a direction parallel tothe reference plane, is greater than the maximum height of a member ofthe population.

Another aspect of the present invention is an electrochemical stack foruse in an energy storage device. The electrochemical stack comprises apopulation of anode structures, cathode structures, and separator layerscomprising a porous dielectric material between the anode structures andthe cathode structures. The anode structures, cathode structures andseparator layers are stacked in a direction substantially parallel to areference plane wherein each anode structure comprises (a) a backbonehaving a lateral surface, the lateral surface being substantiallyperpendicular to the reference plane and having a height of at least 50micrometers measured in a direction that is substantially perpendicularto the surface of the reference plane, and (b) a microstructuredanodically active material layer supported by the lateral surface. Thelineal distance between at least two members of the population, measuredin a direction parallel to the reference plane, is greater than themaximum height of a member of the population. The microstructuredanodically active material layer comprises a back surface, a frontsurface, and a fibrous or porous anodically active material. Themicrostructured anodically active material layer further has a voidvolume fraction of at least 0.1 and a thickness between the back andfront surfaces of at least 1 micrometer, wherein (i) the back surface ofeach such microstructured anodically active material layer is proximatethe lateral surface of the backbone supporting such microstructuredanodically active material layer, (ii) the front surface of each suchmicrostructured anodically active material layer is distal to thelateral surface of the backbone supporting such microstructuredanodically active material layer, (iii) fibers comprised by a member ofthe population of microstructured anodically active material layers areattached to and have central axes that are substantially perpendicularto the back surface of the member comprising such fibers and (iv) porescomprised by a member of the population of microstructured anodicallyactive material layers have pore openings having major axes that aresubstantially parallel to the reference plane.

Another aspect of the present invention is an energy storage devicecomprising carrier ions, a non-aqueous electrolyte and anelectrochemical stack, the carrier ions being lithium, sodium orpotassium ions, the electrochemical stack comprising, in a stackedarrangement, cathode structures, separator layers and anode structures,the separator layers being disposed between the anode structures and thecathode structures. The direction of stacking of the cathode structures,separator layers, and anode structures in the electrochemical stack isparallel to a reference plane. The anode structures comprise apopulation of microstructured anodically active material layers wherein(a) members of the population comprise a fibrous or porous anodicallyactive material and have (i) a surface that is substantiallyperpendicular to the reference plane, (ii) a thickness of at least 1micrometer measured in a direction parallel to the reference plane,(iii) a height of at least 50 micrometers measured in a directionorthogonal to the reference plane, and (iv) a void volume fraction of atleast 0.1. The lineal distance between at least two members of thepopulation, measured in a direction parallel to the reference plane, isgreater than the maximum height of any member of the population ofmicrostructured anodically active material layers.

Another aspect of the present invention is a secondary batterycomprising carrier ions, a non-aqueous electrolyte and at least twoelectrochemical stacks, the carrier ions being lithium, sodium orpotassium ions. Each of the electrochemical stacks comprises, in astacked arrangement, cathode structures, separator layers and anodestructures. The separator layers are disposed between the anodestructures and the cathode structures, and the direction of stacking ofthe cathode structures, the separator layers, and the anode structureswithin each such electrochemical stack is parallel to a reference plane.The anode structures comprise a population of microstructured anodicallyactive material layers wherein (a) members of the population comprise afibrous or porous anodically active material and have (i) a surface thatis substantially perpendicular to the reference plane, (ii) a thicknessof at least 1 micrometer measured in a direction parallel to thereference plane, (iii) a height of at least 50 micrometers measured in adirection orthogonal to the reference plane, and (iv) a void volumefraction of at least 0.1. Additionally, the electrochemical stacks arestacked relative to each other in a direction that is orthogonal to thereference plane.

Other objects and features will be in part apparent and in part pointedout hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a generic cross-section of a cell of an electrochemical stackof an existing two-dimensional energy storage device such as a lithiumion battery.

FIG. 2 is a schematic illustration of two cells of a three-dimensionalenergy storage device of the present invention such as a secondarybattery.

FIG. 3 is a fragmentary, cross-sectional view of an anodically activematerial layer comprising silicon taken along line 3-3 in FIG. 2.

FIGS. 4A-4E are schematic illustrations of some shapes into which anodeand cathode structures may be assembled according to certain embodimentsof the present invention.

FIG. 5 is a fragmentary, cross-sectional view of three die, eachcomprising an electrochemical stack.

FIG. 6 is a view of an anode structure of one of dies of FIG. 5.

FIG. 7 is a fragmentary, cross-sectional view of an anodically activematerial layer comprising porous silicon taken along line 7-7 in FIG. 6.

FIG. 8 is a schematic illustration of a starting material for a step ofmanufacturing an anode backbone and a cathode support structure of thepresent invention.

FIG. 9 is a schematic illustration of an exemplary anode backbone and acathode support structure formed in accordance with one embodiment of aprocess of the present invention.

FIG. 10 is a schematic illustration of a secondary battery of thepresent invention.

FIG. 11 is a schematic view of a 3-dimensional electrochemical stack ofan energy storage device according to an alternative embodiment of thepresent invention.

FIG. 12 is a schematic view of a 3-dimensional electrochemical stack ofan energy storage device according to an alternative embodiment of thepresent invention.

FIG. 13 is a schematic view of an interdigitated 3-dimensionalelectrochemical stack of an energy storage device according to analternative embodiment of the present invention.

FIG. 14 is a photograph of a porous silicon layer on a silicon backboneprepared as described in Example 1.

Corresponding reference characters indicate corresponding partsthroughout the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Among the various aspects of the present invention may be notedthree-dimensional structures offering particular advantages whenincorporated into electrochemical stacks of energy storage devices suchas batteries, capacitors, and fuel cells. For example, such structuresmay be incorporated into secondary batteries in which an anode, acathode, and/or a separator are non-laminar in nature. Advantageously,the surface area for such non-laminar anode structures and cathodestructures may exceed the geometrical footprint of a base supporting theelectrodes by a factor of 1.5, a factor of 2, a factor of 2.5 or even afactor of 3 or more. In one preferred exemplary embodiment, suchstructures are incorporated into secondary batteries in which carrierions selected from lithium, sodium and potassium ions move between theanode and the cathode.

FIG. 2 schematically depicts electrochemical stacks of two cells of athree-dimensional battery in accordance with one embodiment of thepresent invention. For ease of illustration, only one anode structure 24and two cathode structures 26 are depicted in FIG. 2 for each cell 20and only two cells appear in FIG. 2; in practice, however, theelectrochemical stack of each cell will typically comprise a series ofanode and cathode structures extending vertically from a commonreference plane, with the number of anode and cathode structures percell and the number of cells in the battery depending upon theapplication. For example, in one embodiment the number of anodestructures in an electrochemical stack is at least 10. By way of furtherexample in one embodiment the number of anode structures in anelectrochemical stack is at least 50. By way of further example thenumber of anode structures in an electrochemical stack is at least 100.

The electrochemical stack of each cell 20, as depicted, comprises base22, anode structure 24 and cathode structures 26. Each anode structure24 projects vertically (i.e., in the Z-direction as illustrated by theaxes in FIG. 2) from a common reference plane, the surface of base 22(as illustrated) and has a bottom surface B proximate base 22, a topsurface T distal to base 22 and lateral surfaces S₁, S₂ extending fromtop surface T to bottom surface B. Lateral surface S₁ intersects thesurface of base 22 at angle α and lateral surface S₂ intersects thesurface of base 22 at angle δ. In a preferred embodiment, α and δ areapproximately equal and are between about 80° and 100°. For example, inone embodiment, α and δ are approximately equal and are 90°±5°. In aparticularly preferred embodiment, α and δ are substantially the sameand approximately 90°. Independent of the angle of intersection, it isgenerally preferred that the majority of the surface area of each oflateral surfaces S₁ and S₂ is substantially perpendicular to thereference plane, in this embodiment, the surface of base 22; stateddifferently, it is generally preferred that the majority of the surfacearea of each of lateral surfaces S₁ and S₂ lie in a plane (or planes)that intersect(s) the reference plane (the surface of base 22, asillustrated) at an angle between about 80° and 100°, and more preferablyat an angle of 90°±5°. It is also generally preferred that top surface Tbe substantially perpendicular to lateral surfaces S₁ and S₂ andsubstantially parallel to the reference plane, in this embodiment thesurface of base 22. For example, in one presently preferred embodiment,base 22 has a substantially planar surface and anode structure 24 has atop surface T that is substantially parallel to the reference plane,i.e., the planar surface of the base 22 in this embodiment and lateralsurfaces S₁ and S₂ are substantially perpendicular to the referenceplane, i.e., the planar surface of the base 22 in this embodiment.

As illustrated, each anode structure 24 comprises an anode backbone 32having thickness T₃ (measured from surface S₃ to S₄ in a directionparallel to the reference plane, the planar surface of base 22 asillustrated) and anodically active material layers 30, 31 havingthicknesses T₁ (measured from surface S₁ to S₃ in a direction parallelto the reference plane, the planar surface of base 22 as illustrated)and T₂ (measured from surface S₂ to S₄ in a direction parallel to thereference plane, the planar surface of base 22 as illustrated)respectively. During a charging process, lithium (or other carrier)leaves cathode structures 26 and generally travels in the direction ofarrows 23 through a separator (not shown) as lithium ions intoanodically active material layers 30, 31. Depending on the anodicallyactive material used, the lithium ions either intercalate (e.g., sit ina matrix of an anode material without forming an alloy) or form analloy. During a discharge process, the lithium ions (or other carrierions) leave the anodically active material layers 30, 31 and generallytravel in the direction of arrows 21 through the separator (not shown)and into the cathodes 26. As illustrated in FIG. 2, the two cells arearranged vertically (i.e., in the Z-direction, as illustrated) and theshortest distance between the anodically active material layer and thecathode material of an individual cell is measured in a direction thatis parallel to the reference plane, i.e., in this embodiment thesubstantially planar surface of base 22 (i.e., in the X-Y plane asillustrated), and orthogonal to the direction of stacking of the cells(La, in the Z-direction as illustrated). In another embodiment, the twocells are arranged horizontally (i.e., in the X-Y plane, as illustratedin FIG. 2), the shortest distance between the anodically active materiallayer and the cathode material of an individual cell is measured in adirection that is parallel to the reference plane, i.e., in thisembodiment the substantially planar surface of base 22 (i.e., in the X-Yplane as illustrated), and the direction of stacking of the cells isalso parallel to the reference plane (i.e., in the X-Y plane asillustrated in FIG. 2).

Anode backbone 32 provides mechanical stability for anodically activematerial layers 30, 31. Typically, anode backbone 32 will have athickness T₃ (measured from back surface S₃ to back surface S₄ in adirection parallel to the surface of the reference plane, i.e., thesubstantially planar surface of base 22 as illustrated) of at least 1micrometer. Anode backbone 32 may be substantially thicker, butgenerally will not have a thickness in excess of 100 micrometers. Forexample, in one embodiment, anode backbone 32 will have a thickness ofabout 1 to about 50 micrometers. In general, anode backbone will have aheight (as measured in a direction perpendicular to the reference plane,i.e., the substantially planar surface of base 22 as illustrated) of atleast about 50 micrometers, more typically at least about 100micrometers. In general, however, anode backbone 32 will typically havea height of no more than about 10,000 micrometers, and more typically nomore than about 5,000 micrometers. By way of example, in one embodiment,anode backbone 32 will have a thickness of about 5 to about 50micrometers and a height of about 50 to about 5,000 micrometers. By wayof further example, in one embodiment, anode backbone 32 will have athickness of about 5 to about 20 micrometers and a height of about 100to about 1,000 micrometers. By way of further example, in oneembodiment, anode backbone 32 will have a thickness of about 5 to about20 micrometers and a height of about 100 to about 2,000 micrometers.

Depending upon the application, anode backbone 32 may be electricallyconductive or insulating. For example, in one embodiment the anodebackbone 32 may be electrically conductive and may comprise a currentcollector for anodically active material layers 30,31. In one suchembodiment, anode backbone comprises a current collector having aconductivity of at least about 10³ Siemens/cm. By way of furtherexample, in one such embodiment, anode backbone comprises a currentcollector having a conductivity of at least about 10⁴ Siemens/cm. By wayof further example, in one such embodiment, anode backbone comprises acurrent collector having a conductivity of at least about 10⁵Siemens/cm. In other embodiments, anode backbone 32 is relativelynonconductive. For example, in one embodiment, anode backbone 32 has anelectrical conductivity of less than 10 Siemens/cm. By way of furtherexample in one embodiment, anode backbone 32 has an electricalconductivity of less than 1 Siemens/cm. By way of further example in oneembodiment, anode backbone 32 has an electrical conductivity of lessthan 10⁻¹ Siemens/cm.

Anode backbone 32 may comprise any material that may be shaped, such asmetals, semiconductors, organics, ceramics, and glasses. Presentlypreferred materials include semiconductor materials such as silicon andgermanium. Alternatively, however, carbon-based organic materials ormetals, such as aluminum, copper, nickel, cobalt, titanium, andtungsten, may also be incorporated into anode backbone structures. Inone exemplary embodiment, anode backbone 32 comprises silicon. Thesilicon, for example, may be single crystal silicon, polycrystallinesilicon, amorphous silicon or a combination thereof.

Anodically active material layers 30, 31 are microstructured to providea significant void volume fraction to accommodate volume expansion andcontraction as lithium ions (or other carrier ions) are incorporatedinto or leave the anodically active material layers 30, 31 duringcharging and discharging processes. In general, the void volume fractionof the anodically active material layer is at least 0.1. Typically,however, the void volume fraction of the anodically active materiallayer is not greater than 0.8. For example, in one embodiment, the voidvolume fraction of the anodically active material layer is about 0.15 toabout 0.75. By way of the further example, in one embodiment, the voidvolume fraction of the anodically active material layer is about 0.2 toabout 0.7. By way of the further example, in one embodiment, the voidvolume fraction of the anodically active material layer is about 0.25 toabout 0.6.

Depending upon the composition of the microstructured anodically activematerial layer and the method of its formation, the microstructuredanodically active material layers may comprise macroporous, microporousor mesoporous material layers or a combination thereof such as acombination of microporous and mesoporous or a combination of mesoporousand macroporous. Microporous material is typically characterized by apore dimension of less than 10 nm, a wall dimension of less than 10 nm,a pore depth of 1-50 micrometers, and a pore morphology that isgenerally characterized by a “spongy” and irregular appearance, wallsthat are not smooth and branched pores. Mesoporous material is typicallycharacterized by a pore dimension of 10-50 nm, a wall dimension of 10-50nm, a pore depth of 1-100 micrometers, and a pore morphology that isgenerally characterized by branched pores that are somewhat well definedor dendritic pores. Macroporous material is typically characterized by apore dimension of greater than 50 nm, a wall dimension of greater than50 nm, a pore depth of 1-500 micrometers, and a pore morphology that maybe varied, straight, branched or dendritic, and smooth or rough-walled.Additionally, the void volume may comprise open or closed voids, or acombination thereof. In one embodiment, the void volume comprises openvoids, that is, the anodically active material layer contains voidshaving openings at the front surface (surfaces S₁, S₂ as illustrated inFIG. 2) of the anodically active material layer, the void openingsfacing the separator and the cathodically active material and throughwhich lithium ions (or other carrier ions) can enter or leave theanodically active material layer; for example, lithium ions may enterthe anodically active material layer through the void openings afterleaving the cathodically active material and traveling to the anodicallyactive material generally in the direction indicated by arrows 23. Inanother embodiment, the void volume comprises closed voids, that is, theanodically active material layer contains voids that are enclosed byanodically active material. In general, open voids can provide greaterinterfacial surface area for the carrier ions whereas closed voids tendto be less susceptible to solid electrolyte interface (“SEI”) while eachprovides room for expansion of the anodically active material layer uponthe entry of carrier ions. In certain embodiments, therefore, it ispreferred that anodically active material layer comprise a combinationof open and closed voids.

Anodically active material layers 30, 31 comprise an anodically activematerial capable of absorbing and releasing a carrier ion such aslithium. Such materials include carbon materials such as graphite, orany of a range of metals, semi-metals, alloys, oxides and compoundscapable of forming an alloy with lithium. Specific examples of themetals or semi-metals capable of constituting the anode material includetin, lead, magnesium, aluminum, boron, gallium, silicon, indium,zirconium, germanium, bismuth, cadmium, antimony, gold, silver, zinc,arsenic, hafnium, yttrium, and palladium. In one exemplary embodiment,anodically active material layers 30, 31 comprises aluminum, tin, orsilicon, or an oxide thereof, a nitride thereof, a fluoride thereof, orother alloy thereof. In another exemplary embodiment, anodically activematerial layers 30, 31 comprise microstructured silicon or an alloythereof. In one particularly preferred embodiment, anodically activematerial layers 30, 31 comprise porous silicon or an alloy thereof,fibers (e.g., nanowires) of silicon or an alloy thereof, a combinationof porous silicon or an alloy thereof and fibers (e.g., nanowires) ofsilicon or an alloy thereof, or other forms of microstructured siliconor an alloy thereof having a void volume fraction of at least 0.1. Ineach of the embodiments and examples recited in this paragraph andelsewhere in this patent application, the anodically active materiallayer may be monolithic or a particulate agglomerate.

In general, anodically active material layers 30, 31 have front surfacesS₁, S₂, respectively, back surfaces, S₃, S₄, respectively andthicknesses T₁, T₂, respectively (measured in a direction parallel tothe surface of base 22) of at least 1 micrometer. Typically, however,anodically active material layers 30, 31 will each have a thickness thatdoes not exceed 200 micrometers. For example, in one embodiment,anodically active material layers 30, 31 will have a thickness of about1 to about 100 micrometers. By way of further example, in oneembodiment, anodically active material layers 30, 31 will have athickness of about 2 to about 75 micrometers. By way of further example,in one embodiment, anodically active material layers 30, 31 have athickness of about 10 to about 100 micrometers. By way of furtherexample, in one embodiment, anodically active material layers 30, 31have a thickness of about 5 to about 50 micrometers. By way of furtherexample, in one such embodiment, anodically active material layers 30,31 have a thickness of about 1 to about 100 micrometers and containmicrostructured silicon and/or an alloy thereof such as nickel silicide.Additionally, in one embodiment, anodically active material layers 30,31 will have a thickness of about 1 to about 50 micrometers and containmicrostructured silicon and/or an alloy thereof such as nickel silicide.In general, anodically active material layers 30, 31 will have a height(as measured in a direction perpendicular to the reference plane, i.e.,the substantially planar surface of base 22 as illustrated) of at leastabout 50 micrometers, more typically at least about 100 micrometers. Ingeneral, however, anodically active material layers 30, 31 willtypically have a height of no more than about 10,000 micrometers, andmore typically no more than about 5,000 micrometers. By way of example,in one embodiment, anodically active material layers 30, 31 will have athickness of about 1 to about 200 micrometers and a height of about 50to about 5,000 micrometers. By way of further example, in oneembodiment, anodically active material layers 30, 31 will have athickness of about 1 to about 50 micrometers and a height of about 100to about 1,000 micrometers. By way of further example, in oneembodiment, anodically active material layers 30, 31 will have athickness of about 5 to about 20 micrometers and a height of about 100to about 1,000 micrometers. By way of further example, in oneembodiment, anodically active material layers 30, 31 will have athickness of about 10 to about 100 micrometers and a height of about 100to about 1,000 micrometers. By way of further example, in oneembodiment, anodically active material layers 30, 31 will have athickness of about 5 to about 50 micrometers and a height of about 100to about 1,000 micrometers.

In one embodiment, microstructured anodically active material layers 30,31 comprise porous aluminum, tin or silicon or an alloy thereof. Poroussilicon layers may be formed, for example, by anodization, by etching(e.g., by depositing gold, platinum, or gold/palladium on the (100)surface of single crystal silicon and etching the surface with a mixtureof hydrofluoric acid and hydrogen peroxide), or by other methods knownin the art such as patterned chemical etching. Additionally, theanodically active material layer will generally have a porosity fractionof at least about 0.1 but less than 0.8 and have a thickness of about 1to about 100 micrometers. For example, in one embodiment anodicallyactive material layers 30, 31 comprise porous silicon, have a thicknessof about 5 to about 100 micrometers, and have a porosity fraction ofabout 0.15 to about 0.75. By way of further example, in one embodiment,anodically active material layers 30, 31 comprise porous silicon, have athickness of about 10 to about 80 micrometers, and have a porosityfraction of about 0.15 to about 0.7. By way of further example, in onesuch embodiment, anodically active material layers 30, 31 compriseporous silicon, have a thickness of about 20 to about 50 micrometers,and have a porosity fraction of about 0.25 to about 0.6. By way offurther example, in one embodiment anodically active material layers 30,31 comprise a porous silicon alloy (such as nickel silicide), have athickness of about 5 to about 100 micrometers, and have a porosityfraction of about 0.15 to about 0.75. In each of the foregoingembodiments the thickness of the anodically active material layer willtypically exceed the pore depth. Stated differently, the base of thepore (e.g., the surface of the pore proximate anode backbone 32 (seeFIG. 2) will typically not occur at the boundary (i.e., surfaces S₃ andS₄ as depicted in FIG. 2) between the anodically active material layerand the anode backbone; instead, the boundary between the anodicallyactive material layer and the anode backbone will occur at a greaterdepth (e.g., at a greater distance measured in the direction of arrow 23in FIG. 2) from the base of the pore.

Although there may be significant pore-to-pore variation, the pores ofthe porous silicon (or an alloy thereof) have major axes (sometimesreferred to as a central axis) which are predominantly in the directionof the chemical or electrochemical etching process. Referring now toFIG. 3, when anodically active material layer 32 comprises poroussilicon, pores 60 will have major axes 62 that are predominantlyperpendicular to lateral surface S₁ (see FIG. 2) and generally parallelto a reference plane, in this embodiment the planar surface of base 22.Notably, when cells are stacked vertically as illustrated in FIG. 2, themajor axes of the pores are generally orthogonal to the direction ofstacking of the cells (that is, the major axes of the pores lie in theX-Y plane when the direction of stacking is in the Z-direction asillustrated in FIG. 2).

In another embodiment, microstructured anodically active material layers30, 31 comprise fibers of aluminum, tin or silicon, or an alloy thereof.Individual fibers may have a diameter (thickness dimension) of about 5nm to about 10,000 nm and a length generally corresponding to thethickness of the microstructured anodically active material layers 30,31. Fibers (nanowires) of silicon may be formed, for example, bychemical vapor deposition or other techniques known in the art such asvapor liquid solid (VLS) growth and solid liquid solid (SLS) growth.Additionally, the anodically active material layer will generally have aporosity fraction of at least about 0.1 but less than 0.8 and have athickness of about 1 to about 200 micrometers. For example, in oneembodiment anodically active material layers 30, 31 comprise siliconnanowires, have a thickness of about 5 to about 100 micrometers, andhave a porosity fraction of about 0.15 to about 0.75. By way of furtherexample, in one embodiment, anodically active material layers 30, 31comprise silicon nanowires, have a thickness of about 10 to about 80micrometers, and have a porosity fraction of about 0.15 to about 0.7. Byway of further example, in one such embodiment, anodically activematerial layers 30, 31 comprise silicon nanowires, have a thickness ofabout 20 to about 50 micrometers, and have a porosity fraction of about0.25 to about 0.6. By way of further example, in one embodimentanodically active material layers 30, 31 comprise nanowires of a siliconalloy (such as nickel silicide), have a thickness of about 5 to about100 micrometers, and have a porosity fraction of about 0.15 to about0.75.

Although there may be significant fiber-to-fiber variation, nanowires ofaluminum, tin or silicon (or an alloy thereof) have major axes(sometimes referred to as a central axis) which are predominantlyperpendicular to the anode backbone (at the point of attachment of thenanowire to the microstructured anodically active material layer) andparallel to the surface of the base supporting the backbone (See FIG.2). Notably, when cells are stacked vertically as illustrated in FIG. 2,the major axes of the fibers are generally orthogonal to the directionof stacking of the cells.

In another embodiment, microstructured anodically active material layers30, 31 comprise nanowires of silicon or an alloy thereof and poroussilicon or an alloy thereof. In such embodiments, the anodically activematerial layer will generally have a porosity fraction of at least about0.1 but less than 0.8 and have a thickness of about 1 to about 100micrometers as previously described in connection with porous siliconand silicon nanowires.

Referring again to FIG. 2, base 22 serves as a rigid backplane and mayconstitute any of a wide range of materials. For example, base 22 maycomprise a ceramic, a glass, a polymer or any of a range of othermaterials that provide sufficient rigidity to the overall structure. Inone embodiment, base 22 is insulating; for example, base 22 may have anelectrical conductivity of less than 10 Siemens/cm. In one exemplaryembodiment, base 22 may comprise a silicon-on-insulator structure. Insome embodiments, however, base 22 may be removed after theelectrochemical stack is formed.

Referring now to FIGS. 4A-4E, anode structures 24 and cathode structures26 project from the same reference plane, in this embodiment, the planarsurface of base 22 and are alternating in periodic fashion.Additionally, in each of FIGS. 4A-4E, each anode structure 24 containsat least one lateral surface between its bottom and top surfaces asdescribed more fully in connection with FIG. 2 to support a populationof microstructured anodically active material layers 30. For example,when anode structures 24 are in the shape of pillars (FIG. 4A), themicrostructured anodically active material layer extends at leastpartially, and preferably fully about the circumference of the lateralsurface. By way of further example, when anode structures 24 have two(or more) lateral surfaces as illustrated, for example, in FIGS. 4B-4E,the anodically active material layer at least partially covers, andpreferably fully covers, at least one of the lateral surfaces.Additionally, each of the microstructured anodically active materiallayers in the population has a height (measured in a directionperpendicular to base 22) and the layers are disposed such that thedistance between at least two of the layers of the population, e.g.,layers 30A and 30B, measured in a direction that is substantiallyparallel to the planar surface of base 22 is greater than the maximumheight of any of the layers in the population. For example, in oneembodiment, the distance between at least two of the layers of thepopulation, e.g., layers 30A and 30B, is greater than the maximum heightof any of the layers in the population by a factor of at least 2, and insome embodiments substantially more, e.g., by a factor of at least 5 oreven 10. By way of further example, in one embodiment, the distancebetween a majority of the layers of the population is greater than themaximum height of any of the layers in the population by a factor of atleast 2, and in some embodiments substantially more, e.g., by a factorof at least 5 or even 10.

FIG. 4A shows a three-dimensional assembly with anode structures 24 andcathode structures 26 in the shape of pillars. Each of the pillarscomprises a backbone having a lateral surface (not shown) projectingvertically from base 22. The lateral surface of each of the backbonessupports an anodically active material layer 30 and the layers 30 aredisposed such that the distance between at least two of the layers ofthe population, e.g., layers 30A and 30B, is greater than the maximumheight of any of the layers in the population.

FIG. 4B shows a three-dimensional assembly with cathode structures 26and anode structures 24 in the shape of plates. Each of the platescomprises a backbone having a lateral surface (not shown) projectingvertically from base 22. The lateral surface of each of the backbonessupports an anodically active material layer 30 and the layers 30 aredisposed such that the distance between at least two of the layers ofthe population, e.g., layers 30A and 30B, is greater than the maximumheight of any of the layers in the population.

FIG. 4C shows a three-dimensional assembly with cathode structures 26and anode structures 24 in the shape of concentric circles. Each of theconcentric circles comprises a backbone having a lateral surface (notshown) projecting vertically from base 22. The lateral surface of eachof the backbones supports an anodically active material layer 30 and thelayers 30 are disposed such that the distance between at least two ofthe layers of the population, e.g., layers 30A and 30B, is greater thanthe maximum height of any of the layers in the population.

FIG. 4D shows a three-dimensional assembly with cathode structures 26and anode structures 24 in the shape of waves. Each of the wavescomprises a backbone having a lateral surface (not shown) projectingvertically from base 22. The lateral surface of each of the backbonessupports an anodically active material layer 30 and the layers 30 aredisposed such that the distance between at least two of the layers ofthe population, e.g., layers 30A and 30B, is greater than the maximumheight of any of the layers in the population.

FIG. 4E shows a three-dimensional assembly with cathode structures 26and anode structures 24 in a honeycomb pattern. The cathode structures26 are in the shape of pillars at the center of each unit cell of thehoneycomb structure and the walls of each unit cell of the honeycombstructure comprise an interconnected backbone network (system) havinglateral surfaces (not shown) projecting vertically from base 22. Thelateral surfaces of the backbone network (system) support anodicallyactive material layers 30 and the layers 30 are disposed such that thedistance between at least two of the layers of the population, e.g.,layers 30A and 30B, is greater than the maximum height of any of thelayers in the population. In an alternative embodiment, thethree-dimensional assembly is a honeycomb structure, but the relativepositions of the anode structures and cathode structures reversedrelative to the embodiment depicted in FIG. 4E, i.e., in the alternativeembodiment, the anode structures are in the shape of pillars (havinglateral surfaces supporting anodically active material layers) and thewalls of each unit cell comprise cathodically active material.

Independent of the geometry of the anode structures, in one embodimentan electrochromic stack comprises a population of microstructuredanodically active material layers having at least 20 anodically activematerial layers as members. For example, in one embodiment, thepopulation comprises at least 50 members. By way of further example, inone embodiment the population comprises at least 100 members. In otherembodiments, the population may comprise at least 150, at least 200 oreven at least 500 members.

Referring now to FIG. 5, die stack 14 comprises three dies, each die 20comprising a base 22 and an electrochemical stack comprising analternating series of anode structures 24 and cathode structures 26projecting from base 22. Each anode structure 24 comprises anodebackbone 32, microstructured anodically active material layer 31, andanode current collector 28. Each cathode structure 26 comprises cathodematerial 27, cathode current collector 34 and cathode backbone 36.Separator 38 is positioned between each anode structure 24 and eachcathode structure 26. In one embodiment, base 22 is removed and anodestructures 24 and cathode structures 26 project from a common referenceplane parallel to base 22.

For ease of illustration, only two anode structures 24 and only onecathode structure 26 are depicted in FIG. 5 for each die 20 and onlythree die appear in the vertical stack depicted in FIG. 5; in practice,however, each die will typically comprise an electrochemical stackcomprising an alternating series of anode structures and cathodestructures, with the number of anode structures and cathode structuresper electrochemical stack and the number of dies in the vertical stackdepending upon the application. For lithium ion batteries for portableelectronics such as mobile phones and computers, for example, each diemay contain about 20 to about 500 anode structures and an approximatelyequal number of cathode structures. For example, in one embodiment eachdie may contain at least 20, at least 50, at least 100, at least 150, atleast 200 or even at least 500 anode structures and an approximatelyequal number of cathode structures. The size of the die may also varysubstantially depending upon the application. For lithium ion batteriesfor portable electronics such as mobile phones and computers, forexample, each die may have a size of 50 mm (L)×50 mm(W)×5 mm(H).Additionally, in one embodiment the dies are preferably stacked,relative to each other, in a direction that is orthogonal to thedirection of stacking of the anode structures, separator layers, andcathode structures within an electrochemical stack of a die; stateddifferently each die is preferably stacked in a direction that isorthogonal to the substantially planar surface of each base 22 (orcommon reference plane) of an individual die. In one alternativeembodiment, the dies are stacked, relative to each other, in a directionthat is parallel to the direction of stacking of the anode structures,separator layers, and cathode structures within an electrochemical stackof a die; stated differently each die is preferably stacked in adirection that lies within a plane that is parallel to the substantiallyplanar surface of each base 22 (or common reference plane) of anindividual die.

Base 22 serves as a rigid backplane and may constitute any of a widerange of materials. As previously noted, base 22 may comprise a ceramic,a glass, a polymer or any of a range of other materials that providesufficient rigidity and electrical insulation to the overall structure.In one embodiment, base 22 is removed or otherwise omitted (providedsome structure or means are provided to prevent electrical shortingbetween the anode and the cathode structures) and the anode and cathodestructures project from a common reference plane instead of a commonbase.

The overall size of the anode structure 24 may depend, in part, upon theapplication and, in part, upon manufacturing concerns. For lithium ionbatteries for portable electronics such as mobile phones and computers,for example, each anode structure 24 will typically have a height,H_(A), (as measured in a direction perpendicular to base 22) of at leastabout 50 micrometers, more typically at least about 100 micrometers. Ingeneral, however, the anode structure(s) will typically have a height ofno more than about 10,000 micrometers, and more typically no more thanabout 5,000 micrometers. Additionally, the lineal distance between atleast one pair of anodically active material layers 31 of the sameelectrochemical stack 20 preferably exceeds the maximum height, H_(A),of a member of the population of anodically active material layers inthe same electrochemical stack.

Referring again to FIG. 5, each anode structure 24 comprises an anodecurrent collector layer 28 overlying and in contact with anodicallyactive material layer 31 which, in turn, overlies and is contact withanode backbone 32. As carrier ions move between the anodically activematerial and the cathodically active material in such an electrochemicalstack, therefore, they pass through the anode current collector layer 28positioned between the separator and the anodically active materiallayer. In this embodiment, anode current collector layer 28 comprises anion ically permeable conductor that has sufficient ionic permeability tocarrier ions to facilitate the movement of carrier ions from theseparator to the anodically active material layer and sufficientelectrical conductivity to enable it to serve as a current collector.

Being positioned between the anodically active material layer and theseparator, the anode current collector layer may facilitate more uniformcarrier ion transport by distributing current from the anode currentcollector across the surface of the anodically active material layer.This, in turn, may facilitate more uniform insertion and extraction ofcarrier ions and thereby reduce stress in the anodically active materialduring cycling; since the anode current collector layer distributescurrent to the surface of the anodically active material layer facingthe separator, the reactivity of the anodically active material layerfor carrier ions will be the greatest where the carrier ionconcentration is the greatest.

In this embodiment, the anode current collector layer comprises anionically permeable conductor material that is both ionically andelectrically conductive. Stated differently, the anode current collectorlayer has a thickness, an electrical conductivity, and an ionicconductivity for carrier ions that facilitates the movement of carrierions between an immediately adjacent active electrode material layer oneside of the ionically permeable conductor layer and an immediatelyadjacent separator layer on the other side of the anode currentcollector layer in an electrochemical stack. On a relative basis, theanode current collector layer has an electrical conductance that isgreater than its ionic conductance when there is an applied current tostore energy in the device or an applied load to discharge the device.For example, the ratio of the electrical conductance to the ionicconductance (for carrier ions) of the anode current collector layer willtypically be at least 1,000:1, respectively, when there is an appliedcurrent to store energy in the device or an applied load to dischargethe device. By way of further example, in one such embodiment, the ratioof the electrical conductance to the ionic conductance (for carrierions) of the anode current collector layer is at least 5,000:1,respectively, when there is an applied current to store energy in thedevice or an applied load to discharge the device. By way of furtherexample, in one such embodiment, the ratio of the electrical conductanceto the ionic conductance (for carrier ions) of the anode currentcollector layer is at least 10,000:1, respectively, when there is anapplied current to store energy in the device or an applied load todischarge the device. By way of further example, in one such embodiment,the ratio of the electrical conductance to the ionic conductance (forcarrier ions) of the anode current collector layer is at least 50,000:1,respectively, when there is an applied current to store energy in thedevice or an applied load to discharge the device. By way of furtherexample, in one such embodiment, the ratio of the electrical conductanceto the ionic conductance (for carrier ions) of the anode currentcollector layer is at least 100,000:1, respectively, when there is anapplied current to store energy in the device or an applied load todischarge the device.

In one embodiment and when there is an applied current to store energyin the device or an applied load to discharge the device, such as when asecondary battery is charging or discharging, the anode currentcollector layer has an ionic conductance that is comparable to the ionicconductance of an adjacent separator layer. For example, in oneembodiment the anode current collector layer has an ionic conductance(for carrier ions) that is at least 50% of the ionic conductance of theseparator layer (La, a ratio of 0.5:1, respectively) when there is anapplied current to store energy in the device or an applied load todischarge the device. By way of further example, in some embodiments theratio of the ionic conductance (for carrier ions) of the anode currentcollector layer to the ionic conductance (for carrier ions) of theseparator layer is at least 1:1 when there is an applied current tostore energy in the device or an applied load to discharge the device.By way of further example, in some embodiments the ratio of the ionicconductance (for carrier ions) of the anode current collector layer tothe ionic conductance (for carrier ions) of the separator layer is atleast 1.25:1 when there is an applied current to store energy in thedevice or an applied load to discharge the device. By way of furtherexample, in some embodiments the ratio of the ionic conductance (forcarrier ions) of the anode current collector layer to the ionicconductance (for carrier ions) of the separator layer is at least 1.5:1when there is an applied current to store energy in the device or anapplied load to discharge the device. By way of further example, in someembodiments the ratio of the ionic conductance (for carrier ions) of theanode current collector layer to the ionic conductance (for (anodecurrent collector layer) carrier ions) of the separator layer is atleast 2:1 when there is an applied current to store energy in the deviceor an applied load to discharge the device.

In one embodiment, the anode current collector layer also has anelectrical conductance that is substantially greater than the electricalconductance of the anodically active material layer. For example, in oneembodiment the ratio of the electrical conductance of the anode currentcollector layer to the electrical conductance of the anodically activematerial layer is at least 100:1 when there is an applied current tostore energy in the device or an applied load to discharge the device.By way of further example, in some embodiments the ratio of theelectrical conductance of the anode current collector layer to theelectrical conductance of the anodically active material layer is atleast 500:1 when there is an applied current to store energy in thedevice or an applied load to discharge the device. By way of furtherexample, in some embodiments the ratio of the electrical conductance ofthe anode current collector layer to the electrical conductance of theanodically active material layer is at least 1000:1 when there is anapplied current to store energy in the device or an applied load todischarge the device. By way of further example, in some embodiments theratio of the electrical conductance of the anode current collector layerto the electrical conductance of the anodically active material layer isat least 5000:1 when there is an applied current to store energy in thedevice or an applied load to discharge the device. By way of furtherexample, in some embodiments the ratio of the electrical conductance ofthe anode current collector layer to the electrical conductance of theanodically active material layer is at least 10,000:1 when there is anapplied current to store energy in the device or an applied load todischarge the device.

The thickness of the anode current collector layer (i.e., the shortestdistance between the separator and the anodically active material layerbetween which the anode current collector layer is sandwiched) in thisembodiment will depend upon the composition of the layer and theperformance specifications for the electrochemical stack. In general,when an anode current collector layer is an ionically permeableconductor layer, it will have a thickness of at least about 300Angstroms. For example, in some embodiments it may have a thickness inthe range of about 300-800 Angstroms. More typically, however, it willhave a thickness greater than about 0.1 micrometers. In general, anionically permeable conductor layer will have a thickness not greaterthan about 100 micrometers. Thus, for example, in one embodiment, theanode current collector layer will have a thickness in the range ofabout 0.1 to about 10 micrometers. By way of further example, in someembodiments, the anode current collector layer will have a thickness inthe range of about 0.1 to about 5 micrometers. By way of furtherexample, in some embodiments, the anode current collector layer willhave a thickness in the range of about 0.5 to about 3 micrometers. Ingeneral, it is preferred that the thickness of the anode currentcollector layer be approximately uniform. For example, in one embodimentit is preferred that the anode current collector layer have a thicknessnon-uniformity of less than about 25% wherein thickness non-uniformityis defined as the quantity of the maximum thickness of the layer minusthe minimum thickness of the layer, divided by the average layerthickness. In certain embodiments, the thickness variation is even less.For example, in some embodiments the anode current collector layer has athickness non-uniformity of less than about 20%. By way of furtherexample, in some embodiments the anode current collector layer has athickness non-uniformity of less than about 15%. In some embodiments theionically permeable conductor layer has a thickness non-uniformity ofless than about 10%.

In one preferred embodiment, the anode current collector layer is anionically permeable conductor layer comprising an electricallyconductive component and an ion conductive component that contribute tothe ionic permeability and electrical conductivity. Typically, theelectrically conductive component will comprise a continuouselectrically conductive material (such as a continuous metal or metalalloy) in the form of a mesh or patterned surface, a film, or compositematerial comprising the continuous electrically conductive material(such as a continuous metal or metal alloy). Additionally, the ionconductive component will typically comprise pores, e.g., interstices ofa mesh, spaces between a patterned metal or metal alloy containingmaterial layer, pores in a metal film, or a solid ion conductor havingsufficient diffusivity for carrier ions. In certain embodiments, theionically permeable conductor layer comprises a deposited porousmaterial, an ion-transporting material, an ion-reactive material, acomposite material, or a physically porous material. If porous, forexample, the ionically permeable conductor layer may have a voidfraction of at least about 0.25. In general, however, the void fractionwill typically not exceed about 0.95. More typically, when the ionicallypermeable conductor layer is porous the void fraction may be in therange of about 0.25 to about 0.85. In some embodiments, for example,when the ionically permeable conductor layer is porous the void fractionmay be in the range of about 0.35 to about 0.65.

In the embodiment illustrated in FIG. 5, anode current collector layer28 is the sole anode current collector for anodically active materiallayer 31. Stated differently, in this embodiment anode backbone 32 doesnot comprise an anode current collector. In certain other embodiments,however, anode backbone 32 may optionally comprise an anode currentcollector.

Each cathode structure 26 may comprise any of a range of cathode activematerials 27, including mixtures of cathode active materials. Forexample, for a lithium-ion battery, a cathode material, such as LiCoO₂,LiNi_(0.5)Mn_(1.5)O₄, Li(Ni_(x)Co_(y)Al₂)O₂, LiFePO₄, Li₂MnO₄, V₂O₅, andmolybdenum oxysulfides. The cathode active material be deposited to formthe cathode structure by any of a range of techniques including, forexample, electrophoretic deposition, electrodeposition, co-deposition orslurry deposition. In one exemplary embodiment, one of theaforementioned cathode active materials, or a combination thereof, inparticulate form is electrophoretically deposited. In another exemplaryembodiment, a cathode active material such as V₂O₅ is electrodeposited.In another exemplary embodiment, one of the aforementioned cathodeactive materials, or a combination thereof, in particulate form isco-deposited in a conductive matrix such as polyaniline. In anotherexemplary embodiment, one of the aforementioned cathode activematerials, or a combination thereof, in particulate form is slurrydeposited. Independent of the method of deposition, the cathode activematerial layer will typically have a thickness between 1 micron and 1mm. In certain embodiments, the layer thickness is between 5 microns and200 microns, and in certain embodiments, the layer thickness is between10 microns and 150 microns.

Each cathode structure 26 further comprises a cathode current collector34 which, in the embodiment illustrated in FIG. 5, overlies cathodesupport 36. Cathode current collector 34 may comprise any of the metalspreviously identified for the anode current collector; for example, inone embodiment, cathode current collector 34 comprises aluminum, carbon,chromium, gold, nickel, NiP, palladium, platinum, rhodium, ruthenium, analloy of silicon and nickel, titanium, or a combination thereof (see“Current collectors for positive electrodes of lithium-based batteries”by A. H. Whitehead and M. Schreiber, Journal of the ElectrochemicalSociety, 152(11) A2105-A2113 (2005)). By way of further example, in oneembodiment, cathode current collector layer 34 comprises gold or analloy thereof such as gold silicide. By way of further example, in oneembodiment, cathode current collector layer 34 comprises nickel or analloy thereof such as nickel silicide.

Similarly, cathode support 36 may comprise any of the materialspreviously identified for the anode backbone. Presently preferredmaterials include semiconductor materials such as silicon and germanium.Alternatively, however, carbon-based organic materials or metals, suchas platinum, rhodium, aluminum, gold, nickel, cobalt, titanium,tungsten, and alloys thereof may also be incorporated into cathodesupport structures. Typically, the cathode support will have a height ofat least about 50 micrometers, more typically at least about 100micrometers, and any of a range of thicknesses (including the minimum)permitted by the fabrication method being used. In general, however,cathode support 36 will typically have a height of no more than about10,000 micrometers, and more typically no more than about 5,000micrometers. Additionally, in such embodiments, the cathode currentcollector 34 will have a thickness in the range of about 0.5 to 50micrometers.

In an alternative embodiment, the positions of the cathode currentcollector layer and the cathode active material layer are reversedrelative to their positions as depicted in FIG. 5. Stated differently,in some embodiments, the cathode current collector layer is positionedbetween the separator layer and the cathodically active material layer.In such embodiments, the cathode current collector for the immediatelyadjacent cathodically active material layer comprises an ionicallypermeable conductor having a composition and construction as describedin connection with the anode current collector layer; that is, thecathode current collector layer comprises a layer of an ionicallypermeable conductor material that is both ionically and electricallyconductive. In this embodiment, the cathode current collector layer hasa thickness, an electrical conductivity, and an ionic conductivity forcarrier ions that facilitates the movement of carrier ions between animmediately adjacent cathodically active material layer on one side ofthe cathode current collector layer and an immediately adjacentseparator layer on the other side of the cathode current collector layerin an electrochemical stack. On a relative basis in this embodiment, thecathode current collector layer has an electrical conductance that isgreater than its ionic conductance when there is an applied current tostore energy in the device or an applied load to discharge the device.For example, the ratio of the electrical conductance to the ionicconductance (for carrier ions) of the cathode current collector layerwill typically be at least 1,000:1, respectively, when there is anapplied current to store energy in the device or an applied load todischarge the device. By way of further example, in one such embodiment,the ratio of the electrical conductance to the ionic conductance (forcarrier ions) of the cathode current collector layer is at least5,000:1, respectively, when there is an applied current to store energyin the device or an applied load to discharge the device. By way offurther example, in one such embodiment, the ratio of the electricalconductance to the ionic conductance (for carrier ions) of the cathodecurrent collector layer is at least 10,000:1, respectively, when thereis an applied current to store energy in the device or an applied loadto discharge the device. By way of further example, in one suchembodiment, the ratio of the electrical conductance to the ionicconductance (for carrier ions) of the cathode current collector layer isat least 50,000:1, respectively, when there is an applied current tostore energy in the device or an applied load to discharge the device.By way of further example, in one such embodiment, the ratio of theelectrical conductance to the ionic conductance (for carrier ions) ofthe cathode current collector layer is at least 100,000:1, respectively,when there is an applied current to store energy in the device or anapplied load to discharge the device.

When there is an applied current to store energy in the device or anapplied load to discharge the device in this embodiment, such as when asecondary battery is charging or discharging, the cathode currentcollector layer has an ionic conductance that is comparable to the ionicconductance of an adjacent separator layer. For example, in oneembodiment the cathode current collector layer has an ionic conductance(for carrier ions) that is at least 50% of the ionic conductance of theseparator layer (La, a ratio of 0.5:1, respectively) when there is anapplied current to store energy in the device or an applied load todischarge the device. By way of further example, in some embodiments theratio of the ionic conductance (for carrier ions) of the cathode currentcollector layer to the ionic conductance (for carrier ions) of theseparator layer is at least 1:1 when there is an applied current tostore energy in the device or an applied load to discharge the device.By way of further example, in some embodiments the ratio of the ionicconductance (for carrier ions) of the cathode current collector layer tothe ionic conductance (for carrier ions) of the separator layer is atleast 1.25:1 when there is an applied current to store energy in thedevice or an applied load to discharge the device. By way of furtherexample, in some embodiments the ratio of the ionic conductance (forcarrier ions) of the cathode current collector layer to the ionicconductance (for carrier ions) of the separator layer is at least 1.5:1when there is an applied current to store energy in the device or anapplied load to discharge the device. By way of further example, in someembodiments the ratio of the ionic conductance (for carrier ions) of thecathode current collector layer to the ionic conductance (for (cathodecurrent collector layer) carrier ions) of the separator layer is atleast 2:1 when there is an applied current to store energy in the deviceor an applied load to discharge the device.

In this embodiment in which the cathode current collector layer isbetween the cathodically active material layer and the separator, thecathode current collector comprises an ionically permeable conductorlayer having an electrical conductance that is substantially greaterthan the electrical conductance of the cathodically active materiallayer. For example, in one embodiment the ratio of the electricalconductance of the cathode current collector layer to the electricalconductance of the cathodically active material layer is at least 100:1when there is an applied current to store energy in the device or anapplied load to discharge the device. By way of further example, in someembodiments the ratio of the electrical conductance of the cathodecurrent collector layer to the electrical conductance of thecathodically active material layer is at least 500:1 when there is anapplied current to store energy in the device or an applied load todischarge the device. By way of further example, in some embodiments theratio of the electrical conductance of the cathode current collectorlayer to the electrical conductance of the cathodically active materiallayer is at least 1000:1 when there is an applied current to storeenergy in the device or an applied load to discharge the device. By wayof further example, in some embodiments the ratio of the electricalconductance of the cathode current collector layer to the electricalconductance of the cathodically active material layer is at least 5000:1when there is an applied current to store energy in the device or anapplied load to discharge the device. By way of further example, in someembodiments the ratio of the electrical conductance of the cathodecurrent collector layer to the electrical conductance of thecathodically active material layer is at least 10,000:1 when there is anapplied current to store energy in the device or an applied load todischarge the device.

The thickness of the cathode current collector layer (La, the shortestdistance between the separator and the cathodically active materiallayer between which the cathode current collector layer is sandwiched)in this embodiment will depend upon the composition of the layer and theperformance specifications for the electrochemical stack. In general,when a cathode current collector layer is an ionically permeableconductor layer, it will have a thickness of at least about 300Angstroms. For example, in some embodiments it may have a thickness inthe range of about 300-800 Angstroms. More typically, however, it willhave a thickness greater than about 0.1 micrometers. In this embodiment,a cathode current conductor will typically have a thickness not greaterthan about 100 micrometers. Thus, for example, in one embodiment, thecathode current collector layer will have a thickness in the range ofabout 0.1 to about 10 micrometers. By way of further example, in someembodiments, the cathode current collector layer will have a thicknessin the range of about 0.1 to about 5 micrometers. By way of furtherexample, in some embodiments, the cathode current collector layer willhave a thickness in the range of about 1 to about 3 micrometers. Ingeneral, it is preferred that the thickness of the cathode currentcollector layer be approximately uniform. For example, in one embodimentit is preferred that the ionically permeable conductor layer have(cathode current conductor) a thickness non-uniformity of less thanabout 25% wherein thickness non-uniformity is defined as the quantity ofthe maximum thickness of the layer minus the minimum thickness of thelayer, divided by the average layer thickness. In certain embodiments,the thickness variation is even less. For example, in some embodimentsthe cathode current collector layer has a thickness non-uniformity ofless than about 20%. By way of further example, in some embodiments thecathode current collector layer has a thickness non-uniformity of lessthan about 15%. In some embodiments the cathode current collector layerhas a thickness non-uniformity of less than about 10%.

In one preferred embodiment, the cathode current collector layer is anionically permeable conductor layer comprising an electricallyconductive component and an ion conductive component that contribute tothe ionic permeability and electrical conductivity as described inconnection with the anode current collector. Typically, the electricallyconductive component will comprise a continuous electrically conductivematerial (such as a continuous metal or metal alloy) in the form of amesh or patterned surface, a film, or composite material comprising thecontinuous electrically conductive material (such as a continuous metalor metal alloy). Additionally, the ion conductive component willtypically comprise pores, e.g., interstices of a mesh, spaces between apatterned metal or metal alloy containing material layer, pores in ametal film, or a solid ion conductor having sufficient diffusivity forcarrier ions. In certain embodiments, the ionically permeable conductorlayer comprises a deposited porous material, an ion-transportingmaterial, an ion-reactive material, a composite material, or aphysically porous material. If porous, for example, the ionicallypermeable conductor layer may have a void fraction of at least about0.25. In general, however, the void fraction will typically not exceedabout 0.95. More typically, when the ionically permeable conductor layeris porous the void fraction may be in the range of about 0.25 to about0.85. In some embodiments, for example, when the ionically permeableconductor layer is porous the void fraction may be in the range of about0.35 to about 0.65.

In one embodiment, the ionically permeable conductor layer comprised byan electrode current collector layer (i.e., an anode current collectorlayer or a cathode current collector layer) comprises a mesh positionedbetween a separator layer and an electrode active material layer. Themesh has interstices defined by mesh strands of an electricallyconductive material. For example, when electrode active material layeris an anodically active material layer, the mesh may comprise strands ofcarbon, cobalt, chromium, copper, nickel, titanium, or an alloy of oneor more thereof. By way of further example, when electrode activematerial layer is a cathodically active material layer, the mesh maycomprise strands of aluminum, carbon, chromium, gold, NiP, palladium,rhodium, ruthenium, titanium, or an alloy of one or more thereof. Ingeneral, the mesh will have a thickness (i.e., the strands of the meshhave a diameter) of at least about 2 micrometers. In one exemplaryembodiment, the mesh has a thickness of at least about 4 micrometers. Inanother exemplary embodiment, the mesh has a thickness of at least about6 micrometers. In another exemplary embodiment, the mesh has a thicknessof at least about 8 micrometers. In each of the foregoing embodiments,the open area fraction of the mesh (i.e., the fraction of the meshconstituting the interstices between mesh strands) is preferably atleast 0.5. For example, in each of the foregoing embodiments, the openarea fraction of the mesh may be at least 0.6. By way of furtherexample, in each of the foregoing embodiments, the open area fraction ofthe mesh may be at least 0.75. By way of further example, in each of theforegoing embodiments, the open area fraction of the mesh may be atleast 0.8. In general, however, in each of the foregoing embodiments,the ratio of the average distance between the strands of the mesh to thethickness of the electrode active material layer is no more than 100:1,respectively. For example, in each of the foregoing embodiments, theratio of the average distance between the mesh strands to the thicknessof the electrode active material layer is no more than 50:1,respectively. By way of further example, in each of the foregoingembodiments, the ratio of the average distance between the mesh strandsto the thickness of the electrode active material layer is no more than25:1. Advantageously, one or both ends of the mesh may be welded orotherwise connected to metal tabs or other connectors to enablecollected current to be carried to the environment outside the battery.

In one embodiment, the ionically permeable conductor layer comprised byan electrode current collector layer (i.e., an anode current collectorlayer or a cathode current collector layer) comprises a mesh of a metalor an alloy thereof as previously described, and the interstices betweenthe strands of the mesh are open, filled with a porous material that maybe permeated with electrolyte, or they contain a nonporous materialthrough which the carrier ions may diffuse. When filled with a porousmaterial, the porous material will typically have a void fraction of atleast about 0.5, and in some embodiments, the void fraction will be atleast 0.6, 0.7 or even at least about 0.8. Exemplary porous materialsinclude agglomerates of a particulate ceramic such as SiO₂, Al₂O₃, SiC,or Si₃N₄ and agglomerates of a particulate polymer such as polyethylene,polypropylene, polymethylmethacrylates and copolymers thereof. Exemplarynonporous materials that may be placed in the interstices of the meshinclude solid ion conductors such as Na₃Zr₂Si₂PO₁₂ (NASICON),Li_(2+2x)Zn_(1-x)GeO₄ (LISICON), and lithium phosphorous oxynitride(LiPON).

In one embodiment, the ionically permeable conductor layer comprised byan electrode current collector layer (i.e., an anode current collectorlayer or a cathode current collector layer) comprises conductive linesdeposited or otherwise formed on the surface of the immediately adjacentseparator layer or the immediately adjacent electrode active materiallayer (La, the immediately adjacent anodically active material layer orthe immediately adjacent cathodically active material layer). In thisembodiment, the conductive lines may comprise any of the metals (oralloys thereof) previously identified in connection with the meshcomponent. For example, when the ionically permeable conductor layer ispositioned between a separator layer and an anodically active materiallayer, the conductive lines may comprise carbon, cobalt, chromium,copper, nickel, titanium, or an alloy of one or more thereof. When theionically permeable conductor layer is positioned between a separatorlayer and a cathodically active material layer, the conductive lines maycomprise aluminum, carbon, chromium, gold, NiP, palladium, rhodium,ruthenium, titanium, or an alloy of one or more thereof. In general, theconductive lines will have a thickness of at least about 2 micrometers.In one exemplary embodiment, the conductive lines have a thickness of atleast about 4 micrometers. In another exemplary embodiment, theconductive lines have a thickness of at least about 6 micrometers. Inanother exemplary embodiment, the conductive lines have a thickness ofat least about 8 micrometers. In each of the foregoing embodiments, theratio of the average distance between the conductive lines to thethickness of the electrode active material layer is no more than 100:1,respectively. For example, in each of the foregoing embodiments, theratio of the average distance between the conductive lines to thethickness of the electrode active material layer is no more than 50:1,respectively. By way of further example, in each of the foregoingembodiments, the ratio of the average distance between the conductivelines to the thickness of the electrode active material layer is no morethan 25:1, respectively. Advantageously, one or more ends of theconductive lines may be welded or otherwise connected to metal tabs orother connectors to enable collected current to be carried to theenvironment outside the battery.

In one embodiment, the ionically permeable conductor layer comprised byan electrode current collector layer (i.e., an anode current collectorlayer or a cathode current collector layer) comprises a conductive lineof a metal or an alloy thereof as previously described, the spaces onthe surface of the coated material may be open, they may be filled witha porous material that may be permeated with electrolyte, or they maycontain a nonporous material through which the carrier ions may diffuse.When filled with a porous material, the porous material will typicallyhave a void fraction of at least about 0.5, and in some embodiments, thevoid fraction will be at least 0.6, 0.7 or even at least about 0.8.Exemplary porous materials include agglomerates of a particulate ceramicsuch as SiO₂, Al₂O₃, SiC, or Si₃N₄ and agglomerates of a particulatepolymer such as polyethylene, polypropylene, polymethylmethacrylates andcopolymers thereof. Exemplary nonporous materials that may be placedbetween the conductive lines include solid ion conductors such asNa₃Zr₂Si₂PO₁₂ (NASICON), Li_(2+2x)Zn_(1-x)GeO₄ (LISICON), and lithiumphosphorous oxynitride (LiPON).

In one embodiment, the ionically permeable conductor layer comprised byan electrode current collector layer (i.e., an anode current collectorlayer or a cathode current collector layer) comprises a porous layer orfilm such as a porous metal layer. For example when the electrode activematerial layer is an anodically active material layer, the porous layermay comprise a porous layer of carbon, cobalt, chromium, copper, nickel,titanium, or an alloy of one or more thereof. By way of further example,when electrode active material layer is a cathodically active materiallayer, the porous layer may comprise a porous layer of aluminum, carbon,chromium, gold, NiP, palladium, rhodium, ruthenium, titanium, or analloy of one or more thereof. Exemplary deposition techniques for theformation of such porous layers include electroless deposition, electrodeposition, vacuum deposition techniques such as sputtering,displacement plating, vapor deposition techniques such as chemical vapordeposition and physical vapor deposition, co-deposition followed byselective etching, and slurry coating of metal particles with a binder.In general, it is preferred that the void fraction of such porous layersbe at least 0.25. For example, in one embodiment the void fraction of aporous metal layer will be at least 0.4, at least 0.5, at least 0.6, atleast 0.7 and up to about 0.75. To provide the desired electricalconductance, the layer will typically have a thickness of at least about1 micrometer. In some embodiments, the layer will have a thickness of atleast 2 micrometers. In some embodiments, the layer will have athickness of at least 5 micrometers. In general, however, the layer willtypically have a thickness that does not exceed 20 micrometers, and moretypically does not exceed about 10 micrometers. Optionally, such metallayers or films may contain a binder such as polyvinylidene fluoride(PVDF) or other polymeric or ceramic material.

In yet another alternative embodiment, the ionically permeable conductorlayer comprised by an electrode current collector layer (i.e., an anodecurrent collector layer or a cathode current collector layer) comprisesa metal-filled ion conducting polymer composite film. For example, theionically permeable conductor layer may comprise an ionically conductingfilm such as polyethylene oxide or gel polymer electrolytes containing aconductive element such as aluminum, carbon, gold, titanium, rhodium,palladium, chromium, NiP, or ruthenium, or an alloy thereof. Typically,however, solid ion conductors have relatively low ionic conductivityand, thus, the layers need to be relatively thin to provide the desiredionic conductance. For example, such layers may have a thickness in therange of about 0.5 to about 10 micrometers.

In yet another alternative embodiment, the ionically permeable conductorlayer comprised by an electrode current collector layer (i.e., an anodecurrent collector layer or a cathode current collector layer) comprisesa porous layer of a metal or a metal alloy, preferably one which doesnot form an intermetallic compound with lithium. In this embodiment, forexample, the ionically permeable conductor layer may comprise at leastone metal selected from the group consisting of copper, nickel, andchromium, or an alloy thereof. For example, in one such embodiment, theelectrode current collector layer comprises porous copper, porousnickel, a porous alloy of copper or nickel, or a combination thereof. Byway of further example, in one such embodiment, the electrode currentcollector layer comprises porous copper or an alloy thereof such asporous copper silicide. By way of further example, in one suchembodiment, the electrode current collector layer comprises porousnickel or a porous alloy thereof such as porous nickel silicide. In eachof the foregoing embodiments recited in this paragraph, the thickness ofthe electrode current collector layer (i.e., the shortest distancebetween the immediately adjacent electrode active material layer and theimmediately adjacent separator layer) will generally be at least about0.1 micrometers, and typically in the range of about 0.1 to 10micrometers. In each of the foregoing embodiments recited in thisparagraph, the electrode current collector layer may be porous with avoid fraction of in the range of about 0.25 to about 0.85 and, incertain embodiments, in the range of about 0.35 to about 0.45.

In one preferred embodiment, an anode current collector layer is formedby a process comprising a displacement plating step. In this embodiment,anodically active material layer preferably comprises silicon and thelayer is contacted with a solution comprising ions of a metal and adissolution component for dissolving part of the silicon. The silicon isdissolved, the metal in solution is reduced by electrons provided by thedissolution of the silicon, and the metal is deposited on the anodicallyactive material layer, and annealing to form a metal-silicon alloylayer. The “dissolution component” refers to a constituent that promotesdissolution of the semiconductor material. Dissolution componentsinclude fluoride, chloride, peroxide, hydroxide, permanganate, etc.Preferred dissolution components are fluoride and hydroxide. Mostpreferred dissolution component is fluoride. The metal may be any of theaforementioned metals, with nickel and copper being preferred.Advantageously, the resulting layer will be porous, having a voidfraction of about 0.15 to about 0.85. Additionally, the thickness of theresulting ionically permeable conductor layer can be controlled to bebetween about 100 nanometers and 3 micrometers; if desired, thickerlayers can be formed.

Referring again to FIG. 5, separator layer 38 is positioned between eachanode structure 24 and each cathode structure 26. Separator layer 38 maycomprise any of the materials conventionally used as secondary batteryseparators including, for example, microporous polyethylenes,polypropylenes, TiO₂, SiO₂, Al₂O₃, and the like (P. Arora and J. Zhang,“Battery Separators” Chemical Reviews 2004, 104, 4419-4462). Suchmaterials may be deposited, for example, by electrophoretic depositionof a particulate separator material, slurry deposition (including spinor spray coating) of a particulate separator material, or sputtercoating of an ionically conductive particulate separator material.Separator layer 38 may have, for example, a thickness (the distanceseparating an adjacent anodic structure and an adjacent cathodicstructure) of about 5 to 100 micrometers and a void fraction of about0.25 to about 0.75.

In operation, the separator may be permeated with a non-aqueouselectrolyte containing any non-aqueous electrolyte that isconventionally used for non-aqueous electrolyte secondary batteries.Typically, the non-aqueous electrolyte comprises a lithium saltdissolved in an organic solvent. Exemplary lithium salts includeinorganic lithium salts such as LiClO₄, LiBF₄, LiPF₆, LiAsF₆, LiCI, andLiBr; and organic lithium salts such as LiB(C₆H₅)₄, LiN(SO₂CF₃)₂,LiN(SO₂CF₃)₃, LiNSO₂CF₃, LiNSO₂CF₅, LiNSO₂C₄F₉, LiNSO₂C₆F₁₁,LiNSO₂C₆F₁₃, and LiNSO₂C₇F₁₅. Exemplary organic solvents to dissolve thelithium salt include cyclic esters, chain esters, cyclic ethers, andchain ethers. Specific examples of the cyclic esters include propylenecarbonate, butylene carbonate, γ-butyrolactone, vinylene carbonate,2-methyl-γ-butyrolactone, acetyl-γ-butyrolactone, and γ-valerolactone.Specific examples of the chain esters include dimethyl carbonate,diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethylcarbonate, methyl butyl carbonate, methyl propyl carbonate, ethyl butylcarbonate, ethyl propyl carbonate, butyl propyl carbonate, alkylpropionates, dialkyl malonates, and alkyl acetates. Specific examples ofthe cyclic ethers include tetrahydrofuran, alkyltetrahydrofurans,dialkyltetrahydrofurans, alkoxytetrahydrofurans,dialkoxytetrahydrofurans, 1,3-dioxolane, alkyl-1,3-dioxolanes, and1,4-dioxolane. Specific examples of the chain ethers include1,2-dimethoxyethane, 1,2-diethoxythane, diethyl ether, ethylene glycoldialkyl ethers, diethylene glycol dialkyl ethers, triethylene glycoldial kyl ethers, and tetraethylene glycol dialkyl ethers.

Referring now to FIG. 6, anode structure 24 has a bottom surface Bproximate to base 22, a top surface T distal to base 22 and lateralsurfaces S₁, S₂ extending from top surface T to bottom surface B.Lateral surface S₁ intersects the surface of base 22 at angle α andlateral surface S₂ intersects the surface of base 22 at angle δ relativeto the surface of base 22. In a preferred embodiment, a and 5 areapproximately equal and between about 80′ and 100°. For example, in oneembodiment, a and 5 are approximately equal and are 90°±5°. In aparticularly preferred embodiment, a and 5 are substantially the sameand approximately 90°. Independent of the angle of intersection, it isgenerally preferred that the majority of the surface area of each oflateral surfaces S₁ and S₂ is substantially perpendicular to thereference plane, in this embodiment, the surface of base 22; stateddifferently, it is generally preferred that the majority of the surfacearea of each of lateral surfaces S₁ and S₂ lie in a plane (or planes)that intersect(s) the reference plane (the surface of base 22, asillustrated) at an angle between about 80° and 100°, and more preferablyat an angle of 90°±5°. It is also generally preferred that top surface Tbe substantially perpendicular to lateral surfaces S₁ and S₂ andsubstantially parallel to the surface of base 22. For example, in onepresently preferred embodiment, base 22 has a substantially planarsurface and anode structure 24 has a top surface T that is substantiallyparallel to the planar surface of the base 22 and lateral surfaces S₁and S₂ are substantially perpendicular to the planar surface of the base22.

Referring now to FIG. 7, porous layer 31 comprises an anodically activematerial having pores 60 and pore axes 62. In a preferred embodiment,the anodically active material comprises porous silicon or an alloy ofsilicon such as nickel silicide. Although the size, shape and symmetryof pores 60 may be diverse, pore axes 62 will be (i) predominantlyperpendicular to lateral surface S₁ in regions of porous layer 31proximate lateral surface S₁, (ii) predominantly perpendicular tolateral surface S₂ in regions of porous layer 31 proximate lateralsurface S₂, and (iii) predominantly perpendicular to top surface T inregions of porous layer 31 proximate top surface T (see FIG. 6).Accordingly, when lateral surfaces S₁ and S₂ are substantiallyperpendicular to the surface of base 22, pore axes 62 will be (i)predominantly parallel to the surface of base 22 in regions of porouslayer 31 proximate lateral surfaces S₁ and S₂, and (iii) predominantlyperpendicular to the surface of base 22 in regions of porous layer 31proximate top surface T (see FIG. 6). Additionally, in one embodimentthe pore dimension, wall dimension, pore depth and pore morphology inthe region of porous layer 31 that is proximate the top T may differfrom the wall dimension, pore depth and pore morphology in the region ofporous layer 31 proximate surfaces S₁ and S₂.

FIGS. 8-9 depict a schematic representation of one embodiment of aprocess for manufacturing an anode backbone and a cathode support of thepresent invention. Referring now to FIG. 8, a silicon wafer 50 isattached by conventional means to base 22. The base may have the samedimensions as, or may be dimensionally larger or smaller than thesubstrate. For example, wafer 50 and base 22 may be anodically bondedtogether, adhered using an adhesive, or a polymer layer may be formed insitu. As previously noted, base 50 may comprise a layer of a glass,ceramic, polymer or other material that provides sufficient rigidity insubsequent processing steps. Alternatively, a silicon-on-insulator wafermay be used as the starting material.

Referring now to FIG. 9, a photoresist is patterned onto wafer 50 toprovide the desired backbone structures and chemically etched to providean anode backbone and a cathode support. The resulting anode backbone 32has length L_(AB), height H_(AB), and width W_(AB) wherein height H_(AB)is measured in a direction perpendicular to the surface of base 22 andlength L_(AB) and width W_(AB) are measured in a direction that isparallel to the surface of base 22; typically, W_(AB) will be at least 5micrometers, H_(AB) will be at least 50 micrometers and L_(AB) will beat least 1,000 micrometers. The resulting cathode support 36 has lengthL_(CB), height H_(CB), and width W_(CB) wherein height H_(CB) ismeasured in a direction perpendicular to the surface of base 22 andlength L_(CB) and width W_(CB).

After the anode backbone and cathode supports are formed in theillustrated embodiment, cathode support is masked and anode backbone 32is treated to form a layer of microstructured silicon having a voidvolume fraction of at least 0.1 on anode backbone 32 as previouslydescribed. The cathode may then be unmasked and an anode currentcollector is formed on the anodically active material layer and acathode current collector is formed on the cathode support. After acathode material is selectively deposited on the cathode currentcollector, the separator may be deposited between the cathode materialand the anode current collector, the respective current collectors areconnected to battery tabs, and the whole assembly is inserted into aconventional battery pouch, filled with a conventional lithium batteryelectrolyte containing a lithium salt, and a mixture of organiccarbonates (Propylene Carbonate+Ethylene Carbonate), and sealed using avacuum sealer with the wires extending out of the pouch in order to makethe electrical connection. In one alternative embodiment, two or moredie, each containing one or more anodes and one or more cathodesassembled as described are placed in a stack and electrically connectedto battery tabs before the entire assembly is inserted into aconventional battery pouch, etc., to form the battery.

Referring now to FIG. 10, one embodiment of a three-dimensional battery10 of the present invention comprises battery enclosure 12, die stack14, and tabs 16, 18 for electrically connecting die stack 14 to anexternal energy supply or consumer (not shown). For lithium ionbatteries for portable electronics such as mobile phones and computers,for example, battery enclosure 12 may be a pouch or other conventionalbattery enclosure. Die stack 14 comprises several dies, each diecomprising a battery cell having a series of interdigitated anodes andcathodes with the anodes being electrically connected to tab 16 and thecathodes being electrically connected to tab 18. The number of die in avertical stack is not critical and may range, for example, from 1 to 50,with 2 to 20 die in a stack being typical.

Referring now to FIG. 11, in one embodiment an electrochemical stack 610comprises reference plane 601 and backbones 603 projecting generallyvertically from reference plane 601. The cathodic elements ofelectrochemical stack 610 comprise cathode current collector layers 620and cathode active material layers 618. The anodic elements ofelectrochemical stack 610 comprise anodic active material layers 612 andionically permeable conductor layer 614 which also serves as an anodiccurrent collector layer. Preferably, ionically permeable conductor layer614 has a thickness at the top of backbone 603, i.e., the surface ofbackbone distal to reference plane 601, that is greater than thethickness of ionically permeable layer on the lateral sides of backbone603 (the surfaces between the top and reference plane 601); for example,in one embodiment, the thickness of the ionically permeable conductor atthe top of the backbone is 110% to 2,000% of the thickness of theionically permeable conductor on the lateral surfaces. By way of furtherexample, in one embodiment the thickness at the top of the backbone is200% to 1,000% of the thickness of the ionically permeable conductor onthe lateral surfaces. In one embodiment, the permeability of theionically permeable conductor to at the top of the backbone is lesspermeable to carrier ions (e.g., lithium ions) than is the ionicallypermeable conductor on the lateral surfaces, and may even be impermeableto carrier ions. Separator layer 616 is between ionically permeableconductor layer 614 and cathodically active material layers 618. Cathodecurrent collector layers 620 are electrically connected to the cathodecontact (not shown) and ionically permeable conductor layer 614 iselectrically connected to the anode contact (not shown). For ease ofillustration, only one anode backbone and only two cathode backbones aredepicted in FIG. 11; in practice, however, an electrochemical stack willtypically comprise an alternating series of anode and cathode backbones,with the number per stack depending upon the application.

Referring now to FIG. 12, in one embodiment an electrochemical stack 610comprises reference plane 601 and backbones 603 projecting generallyvertically from reference plane 601. The cathodic elements ofelectrochemical stack 610 comprise cathode current collector layers 620and cathode active material layers 618. The anodic elements ofelectrochemical stack 610 comprise anodic active material layers 612 andionically permeable conductor layer 614 which also serves as an anodiccurrent collector layer. Separator layer 616 is between ionicallypermeable conductor layer 614 and cathodically active material layers618. In this embodiment, anodic active material layer 612 is on the topand lateral surfaces of backbone 603 and cathodic active material 618 isproximate the top and lateral surfaces of backbone 603. As a result,during charging and discharging of an energy storage device comprisingelectrochemical stack 610, carrier ions are simultaneously moving in twodirections relative to reference plane 601: carrier ions are moving in adirection generally parallel to reference plane 601 (to enter or leaveanodically active material 612 on the lateral surface of backbone 603)and in a direction generally orthogonal to the reference plane 601 (toenter or leave anodically active material 612 at the top surface ofbackbone 603). Cathode current collector layers 620 are electricallyconnected to the cathode contact (not shown) and ionically permeableconductor layer 614 is electrically connected to the anode contact (notshown). For ease of illustration, only one anode backbone and only twocathode backbones are depicted in FIG. 12; in practice, however, anelectrochemical stack will typically comprise an alternating series ofanode and cathode backbones, with the number per stack depending uponthe application.

Referring now to FIG. 13, in one embodiment an electrochemical stack 710comprises interdigitated anodically active material layers 712 andcathodically material layers 718. The cathodic elements ofelectrochemical stack 710 further comprise cathode current collectorlayer 720 and the anodic elements of the electrochemical stack compriseionically permeable conductor layer 714 which functions as the anodecurrent collector. Separator 716 is between ionically permeableconductor layer 714 and cathodically active material layer 718. Supportlayers 705, 707 provide mechanical support for interdigitated anodicallyactive material layers 712. Although not shown in FIG. 12, in oneembodiment, anodically active material layers 712 and cathodicallyactive material layers 718 and may be supported by backbones, asillustrated in and described in connection with FIG. 2.

The following non-limiting examples are provided to further illustratethe present invention.

EXAMPLES Example 1

A silicon on insulator (SOI) wafer with a layer thickness of 100 μm/1μm/675 μm (device layer/insulating layer/backing layer) was used as thesample. A hard mask layer of 2000 Å silicon dioxide was sputterdeposited on top of the device silicon layer. This wafer was then spincoated with 5 μm of resist and patterned with a mask to obtain ahoneycomb shaped structure with the honeycomb wall thickness of 100 μmand the gap thickness of 200 μm. The photoresist was then used as aphotomask to remove the silicon dioxide by ion milling.

The combination of silicon dioxide and photoresist was used as a maskfor silicon removal using Deep Reactive Ion Etching (DRIE) in a fluorideplasma. The DRIE was performed until the silicon constituting the devicelayer in the honeycomb gaps was completely removed, stopping on theoxide layer. The overetch time used was 10% of the total DRIE time inorder to remove islands of silicon in the trench floor. Any topphotoresist was removed by stripping in acetone.

The top masking oxide layer was removed by dipping the sample for 1minute in dilute (5:1) Buffered Oxide Etch (BOE):water solution. Thedissolution time is tailored so that the insulating oxide layer in thebottom of the trench is not completely etched off.

The silicon sample was then inserted into an evaporation chamber, and100 Å Au is deposited on the sample surface. This process resulted in Auon the top of the honeycomb structures, its sidewalls, as well as on thebottom oxide layer. The silicon backing layer was protected at this timeby an adhesive tape mask. This sample was subsequently immersed in asolution of 1:1 by volume of hydrofluoric acid (49%) and hydrogenperoxide (30%) at 30 C to form a porous silicon layer. The poroussilicon depth was tailored by varying the etching time. The approximaterate of formation of porous silicon was 750-1000 nm/min. The parts wereremoved and dried when the target pore depth of 30 μm was reached. Theresulting porous silicon layer had a void volume fraction ofapproximately 0.3.

The sample was then dried, cross-sectioned and photographed. Asillustrated in FIG. 14 the pores of the dried and cross-sectioned sampleare oriented predominantly in the direction parallel to the base oxidelayer.

Example 2

A silicon on insulator (SOI) wafer with a layer thickness of 100 μm/1μm/675 μm (device layer/insulating layer/backing layer) was used as thesample. 1000 Å of Pd was sputter deposited on top of the device layerfollowed by a hard mask layer of 2000 Å silicon dioxide. This wafer wasthen spin coated with 5 μm of resist and patterned with a mask to obtaina comb shaped structure with two interdigitated combs isolated from eachother as shown in FIG. 3. The two interdigitated combs also have alanding pad on each side that may be isolated and serve as the contactpad for processing and for the final battery. The photoresist was thenused as a photomask to remove the silicon dioxide and palladium by ionmilling.

The combination of silicon dioxide, photoresist, and Pd was used as amask for silicon removal using Deep Reactive Ion Etching (DRIE) in afluoride plasma. The DRIE was performed until the silicon constitutingthe device layer in the mask gaps was completely removed, stopping onthe oxide layer. The overetch time used was 10% of the total DRIE timein order to remove islands of silicon in the trench floor. Any topphotoresist was removed by stripping in acetone. At this point, the twocombs had been electrically isolated by the DRIE.

The top masking oxide layer was removed by dipping the sample for 1minute in dilute (5:1) Buffered Oxide Etch (BOE) solution. Thedissolution time was tailored so that the insulating oxide layer in thebottom of the trench was not completely etched off.

One of the isolated pair of comb like structures was electricallyconnected through the palladium conductor and immersed in anelectrophoretic resist bath. A commercially available electrophoreticresist was used (Shipley EAGLE), and the comb was electrophoreticallydeposited at 50 V for 120 seconds to form a resist coating. The die wasbaked at 120 C for 30 min to harden the resist. This resist acts as aprotection layer during the subsequent metal deposition step.

The silicon sample was then inserted into an evaporation chamber, and100 Å Au was deposited on the sample surface. This Au deposition processresulted in Au on the top of the comb, its sidewalls, and on the bottomoxide layer. However, the photoresist being present on one of the combscauses the Au to be in contact with the silicon on only one of the twocomb structures. The silicon backing layer was also protected at thistime by an adhesive tape mask. This sample was subsequently immersed ina solution of 1:1 by volume of hydrofluoric acid (49%) and hydrogenperoxide (30%), at 30 C to form a porous silicon layer. The poroussilicon depth was tailored by varying the etching time. The approximaterate of formation of porous silicon was 750-1000 nm/min. The parts wereremoved and dried when a the target pore depth of 30 μm was reached. Theresulting porous silicon layer had a void volume fraction ofapproximately 0.3.

The porous silicon was formed only on the comb-set that did not have theelectrophoretic resist patterned onto it. The porous silicon set maythen be used as the anode in a lithium ion battery. The electrophoreticresist was subsequently stripped in acetone for 15 minutes.

Example 3

A silicon on insulator (SOI) wafer with a layer thickness of 100 μm/1μm/675 μm (device layer/insulating layer/backing layer) was used as thesample. 1000 Å of Pd was sputter deposited on top of the device layerfollowed by a hard mask layer of 2000 Å silicon dioxide. This wafer wasthen spin coated with 5 μm of resist and patterned with a mask to obtaina comb shaped structure with two interdigitated combs isolated from eachother as shown in FIG. 3. The two interdigitated combs also have alanding pad on each side that may be isolated and serve as the contactpad for processing and for the final battery. The photoresist was thenused as a photomask to remove the silicon dioxide and Palladium by IonMilling.

The combination of silicon dioxide, photoresist, and Pd was used as amask for silicon removal using Deep Reactive Ion Etching (DRIE) in afluoride plasma. The DRIE was performed until the silicon constitutingthe device layer in the mask gaps was completely removed, stopping onthe oxide layer. The overetch time used was 10% of the total DRIE timein order to remove islands of silicon in the trench floor. Any topphotoresist was removed by stripping in acetone. At this point, the twocombs had been electrically isolated by the DRIE.

The top masking oxide layer was removed by dipping the sample for 1minute in dilute (5:1) Buffered Oxide Etch (BOE) solution. Thedissolution time was tailored so that the insulating oxide layer in thebottom of the trench was not completely etched off.

One of the isolated pair of comb like structures was electricallyconnected through the palladium conductor and immersed in anelectrophoretic resist bath. A commercially available electrophoreticresist was used (Shipley EAGLE), and the comb was electrophoreticallydeposited at 50 V for 120 seconds to form a resist coating. The die wasbaked at 120 C for 30 min to harden the resist.

The silicon sample was then inserted into an evaporation chamber, and 20Å Au is deposited on the sample surface. This Au deposition processresulted in Au on the comb, its sidewalls, as well as on the bottomoxide layer. However, the photoresist being present on one of the combscauses the Au to be in contact with the silicon on only one of the twocomb structures. The silicon backing layer was protected at this time byan adhesive tape mask. The sample was subsequently immersed in acetonefor 15 min to remove the electrophoretic resist alongwith the evaporatedAu on top of the electrophoretic resist. This isolates the Aunanoclusters to one of the two isolated combs.

Silicon nanowires were then grown on top of one of the comb structuresby CVD method. The sample is inserted into a CVD chamber and heated to550 C. Silane gas was introduced into the chamber and the reactorpressure was kept at 10 Torr. The silicon nanowires grew on the surfacethat had the Au deposited on it. The deposition rate was 4 μm/hr; andthe deposition was done to a target nanowire thickness of 20 μm. Sincethe Au was in contact with only one of the silicon wavesets, the wiresstart growing out of this waveset outward, in the direction parallel tothe bottom oxide layer. The resulting silicon nanowire layer had a voidvolume fraction of approximately 0.5.

Example 4

A silicon on insulator (SOI) wafer with a layer thickness of 100 μm/1μm/675 μM (device layer/insulating layer/backing layer) was used as thesample. 1000 Å of Pd was sputter deposited on top of the device layerfollowed by a hard mask layer of 2000 Å silicon dioxide. This wafer wasthen spin coated with 5 μm of resist and patterned with a mask to obtaina comb shaped structure with two interdigitated combs isolated from eachother as shown in FIG. 3. The two interdigitated combs also have alanding pad on each side that will may be isolated and serve as thecontact pad for processing and for the final battery. The photoresistwas then used as a photomask to remove the silicon dioxide and palladiumby ion milling.

The combination of silicon dioxide, photoresist, and Pd was used as amask for silicon removal using Deep Reactive Ion Etching (DRIE) in afluoride plasma. The DRIE was performed until the silicon constitutingthe device layer in the mask gaps was completely removed, stopping onthe oxide layer. The overetch time used was 10% of the total DRIE timein order to remove islands of silicon in the trench floor. Any topphotoresist was removed by stripping in acetone. At this point, the twocombs had been electrically isolated by the DRIE.

A second photoresist was applied on the majority of the wafer, andexposed with a second mask to expose a small area opening on each of thecomb patterns. This was subsequently used to remove the silicon dioxideby ion mill and expose the Pd layer.

The comb structure that was to serve as the anode was immersed in asolution containing HF/H₂O in DMSO (2M/2.5M) and an anodic potential wasapplied with respect to a Pt counter electrode. The silicon comb to beanodically oxidized to form porous silicon was connected through the Pdin the open via. Current density was kept at 3 mA/cm2, and theanodization process was carried out for 60 minutes to yield a pore depthof ˜20 μm. The resulting porous silicon layer had a void volume fractionof approximately 0.4. This process restricted the porous siliconformation to only one of the two comb structures.

Example 5

A silicon on insulator (SOI) wafer with a layer thickness of 100 μm/1μm/675 μm (device layer/insulating layer/backing layer) was used as thesample. 1000 Å of Pd was sputter deposited on top of the device layerfollowed by a hard mask layer of 2000 Å silicon dioxide. This wafer wasthen spin coated with 5 μm of resist and patterned with a mask to obtaina comb shaped structure with two interdigitated combs isolated from eachother. The two interdigitated combs also have a landing pad on each sidethat may be isolated and serve as the contact pad for processing and forthe final battery. The photoresist was then used as a photomask toremove the silicon dioxide and palladium by ion milling.

The combination of silicon dioxide, photoresist, and Pd was used as amask for silicon removal using Deep Reactive Ion Etching (DRIE) in afluoride plasma. The DRIE was performed until the silicon constitutingthe device layer in the mask gaps was completely removed, stopping onthe oxide layer. The overetch time used was 10% of the total DRIE timein order to remove islands of silicon in the trench floor. Any topphotoresist was removed by stripping in acetone. At this point, the twocombs had been electrically isolated by the DRIE.

At this point, the sample was thermally oxidized to form a 0.25 μm layerof SiO₂ on top of all the exposed silicon surfaces. This SiO₂ wasdeposited to serve as the mask for the electrochemical etching ofsilicon. Subsequently, a 50 Å layer of Au was deposited on top of theoxide layer using sputter deposition technique. The thickness of thislayer of Au was optimized in order to obtain Au in the form of islandsand not a full film. This Au in the form of islands was then used as amasking layer for etching the thermal oxide layer under it.

A second photoresist was applied on the majority of the wafer, andexposed with a second mask to expose the landing pad area on each of thecomb patterns. This was subsequently used to remove the Au and SiO₂layers by wet chemical etching. The Au was removed using a commercialKI/I2 solution, and the SiO₂ layer was removed using a Buffered OxideEtch solution in order to expose the Pd top layer for a subsequentelectrical contact.

The sample was then immersed in acetone to strip off the photoresist,and subsequently immersed in 1:25 BOE:water solution. The BOE solutionattacks the SiO₂ layer in the sidewalls of the combs underneath the Auparticle and transfers the pattern of the Au into the oxide. The etchwas stopped after 90 seconds, this being enough to etch the oxide andexpose the Si, while not undercutting the oxide layer under the Au.After rinsing and drying, the sample was ready for electrochemicaldissolution.

The contact pad that had been exposed in the prior step is used to makethe electrical connection for the sample during the silicon anodic etchprocess. This was connected as a working electrode, using a Pt counterelectrode, and was electrochemically driven to dissolve the silicon fromthe exposed area of the connected comb structure. The sample was dippedin a solution containing 1 part ethanol, 1 part 49% HF, and 10 partswater by volume; and was driven as an anode at a current density of 15mA/cm². The exposed silicon was dissolved leaving a microstructuredsilicon layer that replicated the Au nanocluster distribution comprisingfibers and voids and having a void volume fraction of approximately 0.5.

Example 6

A silicon on insulator (SOI) wafer with a layer thickness of 100 μm/1μm/675 μM (device layer/insulating layer/backing layer) was used as thesample. 1000 Å of Pd was sputter deposited on top of the device layerfollowed by a hard mask layer of 2000 Å silicon dioxide.

This wafer was then spin coated with 5 μm of resist and patterned with amask to obtain a comb shaped structure with two interdigitated combsisolated from each other as shown in FIG. 3. The design shows astructure that results in two independent comb shape structures witheach structure terminating in a landing pad suitable for makingelectrical contact. The photoresist in this pattern was then used as aphotomask to remove the silicon dioxide and palladium by ion milling.

The combination of silicon dioxide, photoresist, and Pd was used as amask for silicon removal using Deep Reactive Ion Etching (DRIE) in afluoride plasma. The DRIE was performed until the silicon constitutingthe device layer in the mask gaps was completely removed, stopping onthe oxide layer. The overetch time used was 10% of the total DRIE timein order to remove islands of silicon in the trench floor. Any topphotoresist was removed by stripping in acetone. At this point, the twocombs are electrically isolated by the DRIE.

The top masking oxide layer was subsequently removed by dipping thesample for 1 minute in dilute (5:1) Buffered Oxide Etch (BOE) solution.The dissolution time was tailored so that the insulating oxide layer inthe bottom of the trench was not completely etched off.

One of the isolated pair of comb like structures was electricallyconnected through the palladium conductor and immersed in anelectrophoretic resist bath. A commercially available electrophoreticresist was used (Shipley EAGLE), and the comb was electrophoreticallydeposited at 50 V for 120 seconds to form a resist coating. The die wasbaked at 120 C for 30 min to harden the resist.

The silicon sample was then inserted into an evaporation chamber, and 20Å Au is deposited on the sample surface. This Au deposition processresulted in Au on the top of the honeycomb structures as well as on itssidewalls, as well as on the bottom oxide layer. However, thephotoresist being present on one of the combs causes the Au to be incontact with the silicon on only one of the two comb structures. Thesilicon backing layer was protected at this time by an adhesive tapemask. The sample was subsequently immersed in acetone for 15 min toremove the electrophoretic resist alongwith the evaporated Au on top ofthe electrophoretic resist. This isolated the Au nanoclusters to one ofthe two isolated combs.

Silicon nanowires were then grown on top of one of the comb structuresby CVD method. The sample was inserted into a CVD chamber and heated to550 C. Silane gas was introduced into the chamber and the reactorpressure was kept at 10 Torr. The silicon nanowires grew on the surfacethat had the Au deposited on it. The deposition rate was 4 μm/hr; andthe deposition was done to a target nanowire thickness of 20 μm. Theresulting silicon nanowire layer had a void volume fraction ofapproximately 0.5 and served as the anode for the lithium-ion battery.

The comb without the silicon nanowires attached to it waselectrophoretically deposited with a lithium ion battery cathodematerial. The Electrophoretic deposition solution contained the cathodematerial (LiCoO₂), 15 wt % carbon black, and 150 ppm of iodine in asolution of acetone. The solution mixture was stirred overnight in orderto disperse the particles uniformly. The Pd contact pad was used as theterminal for electrical connection for the cathode deposition. A Ptcounter electrode was used. The sample was deposited for 3 min at avoltage of 100V to deposit a 40 μm thick cathode structure.

The sample was then sent to a spin coater where the macroporousseparator was applied onto the battery. The macroporous separator inthis case was a combination of fine glass powder (<2 μm diameter)dispersed in acetone along with a PVDF binder of 2 volume percent. Thisslurry was coated on to the die and the excess slurry is spun off tofill and planarize the separator layer. The drying process resulted inthe solvent evaporating and forming a macroporous separator layer.

The contact pads were then used to wirebond Au wires to serve asconnection points for the battery. The whole assembly was inserted intoa conventional battery pouch, filled with a conventional lithium batteryelectrolyte containing a lithium salt, and a mixture of organiccarbonates (Propylene Carbonate+Ethylene Carbonate). The pouch was thensealed using a vacuum sealer with the wires extending out of the pouchin order to make the electrical connection.

Example 7

The process of Example 6 was repeated, except that five dies werestacked on top of each other, and each of the lines from the connectionpads from each die was connected to a tab for each electrode.

The whole assembly was inserted into a conventional battery pouch,filled with a conventional lithium battery electrolyte containing alithium salt, and a mixture of organic carbonates (PropyleneCarbonate+Ethylene Carbonate). The pouch was then sealed using a vacuumsealer with the wires extending out of the pouch in order to make theelectrical connection.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

When introducing elements of the present invention or the preferredembodiments(s) thereof, the articles “a”, “an”, “the” and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

As various changes could be made in the above articles, compositions andmethods without departing from the scope of the invention, it isintended that all matter contained in the above description and shown inthe accompanying drawings shall be interpreted as illustrative and notin a limiting sense.

What is claimed is:
 1. A structure for use in an energy storage device,the structure comprising a population of microstructured anodicallyactive material layers, wherein (a) members of the population comprise afibrous or porous anodically active material and have (i) a surface thatis substantially perpendicular to a reference plane, (ii) a thickness,T, of at least 1 micrometer measured in a direction parallel to thereference plane, (iii) a height, H_(A), of at least 50 micrometersmeasured in a direction orthogonal to the reference plane, and (iv) avoid volume fraction of at least 0.1, and (b) the lineal distance,D_(L), between at least two members of the population, measured in adirection parallel to the reference plane, is greater than the maximumvalue of H_(A) for the population.
 2. The structure of claim 1 whereineach member of the population comprises aluminum, tin, silicon or analloy thereof.
 3. The structure of claim 1 wherein each member of thepopulation comprises nanowires of silicon or an alloy thereof, or poroussilicon or an alloy thereof.
 4. The structure of claim 1 wherein eachmember of the population comprises silicon or an alloy thereof and has athickness of about 1 to about 100 micrometers.
 5. The structure of claim1 wherein for each member of the population H_(A) is greater than T. 6.The structure of claim 1 wherein each member of the population comprisesporous silicon or an alloy thereof, has a void volume fraction of atleast 0.1 but less than 0.8, and a thickness of about 1 to about 200micrometers.
 7. The structure of claim 1 wherein the each member of thepopulation is supported by a backbone having an electrical conductivityof less than 10 Siemens/cm.
 8. The structure of claim 1 wherein themaximum value of H_(A) for the population is less than 5,000micrometers.
 9. The structure of claim 1 wherein each member of thepopulation comprises nanowires of silicon or an alloy thereof, or poroussilicon or an alloy thereof, has a void volume fraction of at least 0.1but less than 0.8, a thickness of about 1 to about 200 micrometers, andis supported by a backbone having an electrical conductivity of lessthan 10 Siemens/cm, and the maximum value of H_(A) for the population isless than 5,000 micrometers.
 10. The structure of claim 1 wherein eachmember of the population comprises nanowires of silicon or an alloythereof, or porous silicon or an alloy thereof, has a void volumefraction of at least 0.1 but less than 0.8, a thickness of about 1 toabout 200 micrometers, and is supported by a backbone having anelectrical conductivity of less than 1 Siemens/cm, and the maximum valueof H_(A) for the population is less than 1,000 micrometers.
 11. Thestructure of claim 1 wherein the population comprises at least 20members.
 12. An electrochemical stack for use in an energy storagedevice, the electrochemical stack comprising, in a stacked arrangement,cathode structures, separator layers and anode structures, the separatorlayers being disposed between the anode structures and the cathodestructures, the direction of stacking of the cathode structures, theseparator layers, and the anode structures being parallel to a referenceplane, the anode structures comprising a population of microstructuredanodically active material layers wherein (a) members of the populationcomprise a fibrous or porous anodically active material and have (i) asurface that is substantially perpendicular to the reference plane, (ii)a thickness, T, of at least 1 micrometer measured in a directionparallel to the reference plane, (iii) a height, H_(A), of at least 50micrometers measured in a direction orthogonal to the reference plane,and (iv) a void volume fraction of at least 0.1, and (b) the linealdistance, D_(L), between at least two members of the population,measured in a direction parallel to the reference plane, is greater thanthe maximum value of H_(A) for the population.
 13. The electrochemicalstack of claim 12 wherein the population comprises at least 20 members.14. The electrochemical stack of claim 12 wherein each member of thepopulation comprises nanowires of silicon or an alloy thereof, or poroussilicon or an alloy thereof.
 15. The electrochemical stack of claim 12wherein each member of the population comprises silicon or an alloythereof and has a thickness of about 1 to about 100 micrometers.
 16. Theelectrochemical stack of claim 12 wherein for each member of thepopulation H_(A) is greater than T.
 17. The electrochemical stack ofclaim 12 wherein each member of the population comprises porous siliconor an alloy thereof, has a void volume fraction of at least 0.1 but lessthan 0.8, and a thickness of about 1 to about 200 micrometers.
 18. Theelectrochemical stack of claim 12 wherein each member of the populationcomprises nanowires of silicon or an alloy thereof, or porous silicon oran alloy thereof, has a void volume fraction of at least 0.1 but lessthan 0.8, a thickness of about 1 to about 200 micrometers, and issupported by a backbone and the maximum value of H_(A) for thepopulation is less than 5,000 micrometers.
 19. The electrochemical stackof claim 12 wherein each member of the population comprises nanowires ofsilicon or an alloy thereof, or porous silicon or an alloy thereof, hasa void volume fraction of at least 0.1 but less than 0.8, a thickness ofabout 1 to about 200 micrometers, and is supported by a backbone havingan electrical conductivity of less than 10 Siemens/cm, and the maximumvalue of H_(A) for the population is less than 1,000 micrometers. 20.The electrochemical stack of claim 12 wherein the anode structurescomprise an anode current collector, the cathode structures comprise acathode current collector, and the anode current collector or thecathode current collector comprises an ionically permeable conductorlayer.
 21. The electrochemical stack of claim 12 wherein the anodestructures comprise an anode current collector layer and the anodecurrent collector layer is disposed between the anodically activematerial layer and a separator layer.
 22. The electrochemical stack ofclaim 21 wherein each member of the population comprises nanowires ofsilicon or an alloy thereof, or porous silicon or an alloy thereof, hasa void volume fraction of at least 0.1 but less than 0.8, a thickness ofabout 1 to about 200 micrometers, and is supported by a backbone and themaximum value of H_(A) for the population is less than 5,000micrometers.
 23. The electrochemical stack of claim 12 wherein thecathode structures comprise a cathode current collector layer and thecathode current collector layer is disposed between the cathodicallyactive material layer and a separator layer.
 24. An energy storagedevice comprising carrier ions, a non-aqueous electrolyte and anelectrochemical stack, the carrier ions being lithium, sodium orpotassium ions, the electrochemical stack comprising, in a stackedarrangement, cathode structures, separator layers and anode structures,the separator layers being disposed between the anode structures and thecathode structures, the direction of stacking of the cathode structures,the separator layers, and the anode structures being parallel to areference plane, the anode structures comprising a population ofmicrostructured anodically active material layers wherein (a) members ofthe population comprise a fibrous or porous anodically active materialand have (i) a surface that is substantially perpendicular to thereference plane, (ii) a thickness, T, of at least 1 micrometer measuredin a direction parallel to the reference plane, (iii) a height, H_(A),of at least 50 micrometers measured in a direction orthogonal to thereference plane, and (iv) a void volume fraction of at least 0.1, and(b) the lineal distance, D_(L), between at least two members of thepopulation, measured in a direction parallel to the reference plane, isgreater than the maximum value of H_(A) for the population.
 25. Theenergy storage device of claim 24 wherein the carrier ions are lithiumions.
 26. The energy storage device of claim 24 wherein the populationcomprises at least 20 members.
 27. The energy storage device of claim 24wherein each member of the population comprises silicon or an alloythereof and has a thickness of about 1 to about 100 micrometers.
 28. Theenergy storage device of claim 24 wherein for each member of thepopulation H_(A) is greater than T.
 29. The energy storage device ofclaim 24 wherein each member of the population comprises nanowires ofsilicon or an alloy thereof, or porous silicon or an alloy thereof. 30.The energy storage device of claim 24 wherein each member of thepopulation comprises porous silicon or an alloy thereof, has a voidvolume fraction of at least 0.1 but less than 0.8, and a thickness ofabout 1 to about 200 micrometers.
 31. The energy storage device of claim24 wherein each member of the population comprises nanowires of siliconor an alloy thereof, or porous silicon or an alloy thereof, has a voidvolume fraction of at least 0.1 but less than 0.8, a thickness of about1 to about 200 micrometers, and is supported by a backbone and themaximum value of H_(A) for the population is less than 5,000micrometers.
 32. The energy storage device of claim 24 wherein eachmember of the population comprises nanowires of silicon or an alloythereof, or porous silicon or an alloy thereof, has a void volumefraction of at least 0.1 but less than 0.8, a thickness of about 1 toabout 200 micrometers, and is supported by a backbone having anelectrical conductivity of less than 10 Siemens/cm, and the maximumvalue of H_(A) for the population is less than 1,000 micrometers. 33.The energy storage device of claim 24 wherein the anode structurescomprise an anode current collector, the cathode structures comprise acathode current collector, and the anode current collector or thecathode current collector comprises an ionically permeable conductorlayer.
 34. The energy storage device of claim 24 wherein the anodestructures comprise an anode current collector layer and the anodecurrent collector layer is disposed between the anodically activematerial layer and a separator layer.
 35. The energy storage device ofclaim 34 wherein each member of the population comprises nanowires ofsilicon or an alloy thereof, or porous silicon or an alloy thereof, hasa void volume fraction of at least 0.1 but less than 0.8, a thickness ofabout 1 to about 200 micrometers, and is supported by a backbone and themaximum value of H_(A) for the population is less than 5,000micrometers.
 36. A secondary battery comprising carrier ions, anon-aqueous electrolyte and at least two electrochemical stacks, thecarrier ions being lithium, sodium or potassium ions, each of theelectrochemical stacks comprising, in a stacked arrangement, cathodestructures, separator layers and anode structures, the separator layersbeing disposed between the anode structures and the cathode structures,the direction of stacking of the cathode structures, the separatorlayers, and the anode structures with each such electrochemical stackbeing parallel to a reference plane, the anode structures comprising apopulation of microstructured anodically active material layers wherein(a) members of the population comprise a fibrous or porous anodicallyactive material and have (i) a surface that is substantiallyperpendicular to the reference plane, (ii) a thickness, T, of at least 1micrometer measured in a direction parallel to the reference plane,(iii) a height, H_(A), of at least 50 micrometers measured in adirection orthogonal to the reference plane, and (iv) a void volumefraction of at least 0.1, the electrochemical stacks being stackedrelative to each other in a direction that is orthogonal to thereference plane.
 37. The secondary battery of claim 36 wherein thecarrier ions are lithium ions.
 38. The secondary battery of claim 36wherein the population comprises at least 20 members.
 39. The secondarybattery of claim 36 wherein each member of the population comprisesnanowires of silicon or an alloy thereof, or porous silicon or an alloythereof.
 40. The secondary battery of claim 36 wherein each member ofthe population comprises silicon or an alloy thereof and has a thicknessof about 1 to about 100 micrometers.
 41. The secondary battery of claim36 wherein for each member of the population H_(A) is greater than T.42. The secondary battery of claim 36 wherein each member of thepopulation comprises porous silicon or an alloy thereof, has a voidvolume fraction of at least 0.1 but less than 0.8, and a thickness ofabout 1 to about 200 micrometers.
 43. The secondary battery of claim 36wherein each member of the population comprises nanowires of silicon oran alloy thereof, or porous silicon or an alloy thereof, has a voidvolume fraction of at least 0.1 but less than 0.8, a thickness of about1 to about 200 micrometers, and is supported by a backbone and themaximum value of H_(A) for the population is less than 5,000micrometers.
 44. The secondary battery of claim 36 wherein each memberof the population comprises nanowires of silicon or an alloy thereof, orporous silicon or an alloy thereof, has a void volume fraction of atleast 0.1 but less than 0.8, a thickness of about 1 to about 200micrometers, and is supported by a backbone having an electricalconductivity of less than 10 Siemens/cm, and the maximum value of H_(A)for the population is less than 1,000 micrometers.
 45. The secondarybattery of claim 36 wherein the anode structures comprise an anodecurrent collector, the cathode structures comprise a cathode currentcollector, and the anode current collector or the cathode currentcollector comprises an ionically permeable conductor layer.
 46. Thesecondary battery of claim 36 wherein the anode structures comprise ananode current collector layer and the anode current collector layer isdisposed between the anodically active material layer and a separatorlayer.
 47. The secondary battery of claim 36 wherein each member of thepopulation comprises nanowires of silicon or an alloy thereof, or poroussilicon or an alloy thereof, has a void volume fraction of at least 0.1but less than 0.8, a thickness of about 1 to about 200 micrometers, andis supported by a backbone and the maximum value of H_(A) for thepopulation is less than 5,000 micrometers.